Can't access internal hard drive

These steps are taken from the support site as always, it's the first website where you should look.

Solution 1: Disconnect and reconnect cables
Here's how:

1. Turn off your Xbox 360 console.
2. Unplug all memory units, controllers, and accessories from your console.
3. Unplug everything from the back of your console, including power and video cables.

Don't remove the hard drive.

1. Reconnect your console's power supply.
2. Reconnect each accessory one at a time, starting with a controller.
3. After you've reconnected every accessory, turn the console on.

Solution 2: Remove the hard drive
To see whether the problem involves the original Xbox 360 Hard Drive, temporarily remove the hard disk drive. Here's how.
Note Not all Xbox 360 consoles include a hard drive. If your Xbox 360 console doesn't have a hard drive, to go Solution 3.

1. Turn off the console.
2. Locate the hard drive on the top of the console (or on the left side, depending on how the console is oriented).

• 
• Press the release button on the hard drive.

• Lift the hard drive away from the console.

If these steps resolve the issue, reattach the hard drive to verify that the error occurs only when your Xbox 360 Hard Drive is connected.

Solution 3: Disconnect memory units or USB flash drives
Here's how:

1. Turn off your Xbox 360 console.
2. Unplug any memory units or USB flash drives attached to your console.
3. Turn on the console.

If these steps resolve the problem, reattach the memory unit or USB flash drive to make sure the error occurs only when it's connected. If this is true, order a replacement memory unit or use another USB flash drive.

Solution 4: Request a repair
If the previous steps don't resolve the single flashing red light issue, there are no additional troubleshooting steps. Your original Xbox 360 console must be repaired at our service center. Start the repair process online.

Well if they're flashing the hard drive is over heating and you need to get either a new hard drive or a new Xbox.

The Xbox 360 can only recognize drives up to 16GB as noted on their website, I myself have tried a 32GB flash drive to test the limitations and it was not recognized. At this time it seems as though microsoft is limiting their external storage to 16GB.
http://support.xbox.com/en-us/Pages/xbox-360/how-to/usb-flash-drive.aspx

one red light flashing on the ROL of your Xbox 360 console that's an indicator of a hardware problem with the console connection to one of the parts connected to it as the hard drive or cables. first disconnect all power and AV cables from the back of your Xbox 360 console and also unplug the power cord from the wall socket, wait for a minute then reconnect them all back and try to turn on your Xbox 360 console once more. If that doesn't work, it seems then to be a fault with your Xbox 360 hard drive so turn off the console again and remove the hard drive then turn on your Xbox 360 console without the hard drive, supposed then to work fine, it might be an intermittent issue and when you reconnect the hard drive your Xbox 360 will work fine all after, or it will just work fine without the hard drive so it will be then definitely a fault with your Xbox 360 hard drive so call Xbox 360 customer support to exchange the hard drive for you. The Xbox 360 console might even keep giving you the same error code even after you remove the hard drive so it will then appear to be a fault with your Xbox 360 console not the hard drive & also in a case like this we need to contact Xbox 360 customer support to exchange the console.

read the book menu

E79 is a hard drive problem. It could be a problem with the Hard Drive itself or a problem with the internal connection to the hard drive, Try removing the hard drive and playing without it

Section 4 is flashing red Means
- Hardware Failure
The Specific Type of hardware failure can be determined by the error code displayed on the screen.
If the screen is blank or you would like additional information follow the instructions for determining the secondary error code in the section below

E64: (not yet known)

E65: DVD Drive Error.... DVD Timeout, Wrong firmware, dvd is without f/w chip, etc.

E67: Hard Drive Error... It could be a problem with the Hard Drive itself or a problem with the internal connection to the hard drive, Try removing the hard drive and playing without it

E68: Hard Drive Error... It could be a problem with the Hard Drive itself or a problem with the internal connection to the hard drive, Try removing the hard drive and playing without it, This can also be caused by a Hard Drive Eprom Error.

E69: Hard Drive Error... It could be a problem with the Hard Drive itself or a problem with the internal connection to the hard drive, Try removing the hard drive and playing without it

E71: (not yet known)

E73: (not yet known)

E74: AV cable error... There is a problem with the AV cable, try using a different AV cable. (could also be a problem with the encoder chip)

E76: (not yet known)

E79: Hard Drive Error... It could be a problem with the Hard Drive itself or a problem with the internal connection to the hard drive, Try removing the hard drive and playing without it

=============================

--==SECONDARY ERROR CODES==-
The specific type of hardware failure can be determined by a "hidden" error code

• Turn the xbox 360 on, and wait till the 3 red lights are flashing.
• Press and hold the sync up button (the small white one), while holding that button press the eject button.
• The LEDs will now blink the first number in the code (as described below).
• Release the eject button and press it again.
• The LEDs will now blink the second number of the code.
• Release the eject button and press it again.
• The LEDs will now blink the third number of the code.
• Release the eject button and press it again.
• The LEDs will now blink the forth number of the code.
• Release the eject button and press it again.
• The LEDs will go back to the 3 red flashing lights.

You should be able to determine the difference between the 3 flashing lights and the error code lights by the rate in which they flash.

Here is how you interpret the LEDs to get the code number:

• All four lights flashing - 0
• One light flashing - 1
• Two Lights flashing - 2
• Three lights flashing - 3

0001 power supply problem
0002 power supply problem
0003 (not yet known)
...
0010 over heating
0011 over heating
0012 over heating
0013 over heating
...
0020 (Not yet known, possibly overheating)
0021 (not yet known)
0022 GPU Error / GPU Overheating
...
0101 (not yet known)
0102 unknown error - literally means the console does not know what is wrong. Possibly a short or cold solder joint somewhere (2 reports of people repairing this, one was removing moisture build up inside the console, the other used a hot-air rework to reflow the BGA Ram chips)
...
0110 Memory Error / Memory Overheating
...
1003 Hard Drive Error... It could be a problem with the Hard Drive itself or a problem with the internal connection to the hard drive, Try removing the hard drive and playing without it
...
1010 Hard Drive Error, Can be caused buy a currupt or missing Eprom.
...
1013 (not yet known)
...
1020 (not yet known)
...
1022 AV cable error... There is a problem with the AV cable, try using a different AV cable. (could also be a problem with the encoder chip)
...
1030 (not yet known)

if your console comes up with ANY OF THESE CODES CALL MICROSOFT and they will repair anything for free

3 Red light errors are common with XBOX consoles, and are proven to be fixable!
I run a repair shop and get atleast 1 - 2 consoles in a week with the same problems! and I fix 99% of the consoles with this problem using the XBOX360 Repair Guide, available on google for instant download. You can get your copy from here and fix all common probelms with XBOX console!

This is taken off of teamxbox.com

It is an explanation of the bottom right light blinking red, how to tell exactly what it is, and so on. If there is general hardware failure on your xbox, microsoft posted on their site that you send it in for free repair and also get 3 year extension to your warranty.

Use this guide to determine exactly what is wrong, what hardware is failing, and hopefully we can figure something out. Please get back with me when you can, I would really like to get you up and running again, cause I know how it was when I couldnt play my xbox, I hated it. Good luck!

______________________________________________________

Section 4 is flashing red
- Hardware Failure


The Specific Type of hardware failure can be determined by the error code displayed on the screen.
If the screen is blank or you would like additional information follow the instructions for determining the secondary error code in the section below

E64: (not yet known)

E65: DVD Drive Error.... DVD Timeout, Wrong firmware, dvd is without f/w chip, etc.

E67: Hard Drive Error... It could be a problem with the Hard Drive itself or a problem with the internal connection to the hard drive, Try removing the hard drive and playing without it

E68: Hard Drive Error... It could be a problem with the Hard Drive itself or a problem with the internal connection to the hard drive, Try removing the hard drive and playing without it, This can also be caused by a Hard Drive Eprom Error.

E69: Hard Drive Error... It could be a problem with the Hard Drive itself or a problem with the internal connection to the hard drive, Try removing the hard drive and playing without it

E71: (not yet known)

E73: (not yet known)

E74: AV cable error... There is a problem with the AV cable, try using a different AV cable. (could also be a problem with the encoder chip)

E76: (not yet known)

E79: Hard Drive Error... It could be a problem with the Hard Drive itself or a problem with the internal connection to the hard drive, Try removing the hard drive and playing without it

=============================

--==SECONDARY ERROR CODES==-
The specific type of hardware failure can be determined by a "hidden" error code

• Turn the xbox 360 on, and wait till the 3 red lights are flashing.
• Press and hold the sync up button (the small white one), while holding that button press the eject button.
• The LEDs will now blink the first number in the code (as described below).
• Release the eject button and press it again.
• The LEDs will now blink the second number of the code.
• Release the eject button and press it again.
• The LEDs will now blink the third number of the code.
• Release the eject button and press it again.
• The LEDs will now blink the forth number of the code.
• Release the eject button and press it again.
• The LEDs will go back to the 3 red flashing lights.

You should be able to determine the difference between the 3 flashing lights and the error code lights by the rate in which they flash.

Here is how you interpret the LEDs to get the code number:

• All four lights flashing - 0
• One light flashing - 1
• Two Lights flashing - 2
• Three lights flashing - 3

0001 power supply problem
0002 power supply problem
0003 (not yet known)
...
0010 over heating
0011 over heating
0012 over heating
0013 over heating
...
0020 (Not yet known, possibly overheating)
0021 (not yet known)
0022 GPU Error / GPU Overheating
...
0101 (not yet known)
0102 unknown error - literally means the console does not know what is wrong. Possibly a short or cold solder joint somewhere (2 reports of people repairing this, one was removing moisture build up inside the console, the other used a hot-air rework to reflow the BGA Ram chips)
...
0110 Memory Error / Memory Overheating
...
1003 Hard Drive Error... It could be a problem with the Hard Drive itself or a problem with the internal connection to the hard drive, Try removing the hard drive and playing without it
...
1010 Hard Drive Error, Can be caused buy a currupt or missing Eprom.
...
1013 (not yet known)
...
1020 (not yet known)
...
1022 AV cable error... There is a problem with the AV cable, try using a different AV cable. (could also be a problem with the encoder chip)
...
1030 (not yet known)

3 red lights normally means there is a general hardware failure.

Are the lights flashing?

Turn off the xbox and...

Try unplugging everything from your xbox, plug it back in and turn it on.

if that doesnt work, when your xbox is turned off, take the hard drive out and restart your xbox. If it works with the hard drive, try restarting it again after putting the hard drive back in.