Iphone will not turn on, if I connect it to my computer it makes a noise but nothing happens on the screen, I have tried holding down the on/off and the home buttons.

Download the latest iTunes to your computer and reset the iPhone. Then re-sync it.

Reset

To reset iPhone, press and hold the Sleep/Wake button and the Home button at the same time for at least 10 seconds. During this time, a red "power off" slider may appear and the screen may go black, but do not release Sleep/Wake and Home buttons until the Apple logo appears.

If iPhone won't turn on, or the display freezes or doesn't respond

1. Press and hold the Home button for at least six seconds, until the application you were using quits.
2. If that doesn't work, turn iPhone off and turn it on again. Press and hold the Sleep/Wake button on top of iPhone for a few seconds until a red slider appears, and then slide the slider. Then press and hold the Sleep/Wake button until the Apple logo appears.
3. If that doesn't work, reset iPhone. Press and hold the Sleep/Wake button and the Home button at the same time for at least ten seconds, until the Apple logo appears

More resets:

Try This:
1. Remove Sim Card
2. Hold in 'Home' button and 'On/Off' button together until Apple logo appears
3. Replace Sim Card
4. Hold in 'Home' button and 'On/Off' button together until normal phone screen appears.


Also, Try this:
1.) Shut down the iPhone 3G.
2.) Start up iTunes
3.) Hold down HOME button on the iPhone 3G
4.) While keeping the HOME button depressed, plug in the Sync cable
5.) A message will pop up to ask if you want to reset.
6.) Just click YES and the reset process should start.

I’m happy to assist further over the phone at https://www.6ya.com/expert/joe_8b8c2cd6ce148309