How to diagnose a hard drive

There are several reasons for slow boot time, things you should check.
1- How many programs are in startup?Limit startups to only what is needed, the rest can start using manual or delayed.
2-Malware= Try scanning with Malwarebytes its free :)
3-Virus= Run a complete scan of you hard drive there are many free anti virus programs to choose from.
4- Defrag- your drive often at least monthly.... again many freeware programs to choose from.
Doing this maintenance should help the computer run much better and speed up boot time.

Please explain in detail what happens when you turn the computer on. Do you hear the fans come on? do you hear the hard drive trying to boot? please give me more details and I will try to diagnose the screen issue. Oh and just in case here is a link to the owners manual. http://www.manualslib.com/products/Hp-Pavilion-Dm4-2180-2341384.html

Fans, mainly the CPU fan, have a speed control which slows the fan down. This is usually controlled by the BIOS. The speed is based on temperature of the CPU. If it's cool with little load the CPU fan will run very slowly and you won't be able to hear it. On startup all fans ramp up to 100% until the BIOS takes over and slows the fan down.

Do you hear the fans running? Do you hear the hard drive spinning? Did anything ever appear on the monitor?

Remove the Power Cord, Open the Case and remove one of thememory chips. Set the chip aside then try rebooting the computer. If it boots, then you know the memory chip you set aside is bad so mark an x onit with an ink pen. If it fails to boot then move the chip to the nextmemory slot and try rebooting. If it fails take the chip out and set itaside, then put the other chip in and try booting it in both slots. If itboots, just to verify that the chip set aside is bad, mark an x on it and putit into the open memory chip slot and try booting.

if boot up but slow, you have tot test memory amount and speed and temperature of cpu cooler. if your hard drive is not have 100% smart feature test result, may be slow down. it is rarely with power problem. but you can test with another AC Adapter.

hi Jamiekom.
Slow Running Computer Fix. Use MSCONFIG to improve computer's speed at startup. You can disable certain programs that auto-start at startup and spend less time waiting for your computer to fully boot. Simple tip to improve your computer's performance.
Why is computer so slow to startup? My Windows computer boots up slow. A slow Microsoft Windows boot up can be caused by a number of different issues. The following document contains various suggestions and tips that can help improve the overall speed of your computer's startup.
Why does it take so long to boot up my computer?3. Upgrade your hardware. A new computer is naturally going to start up faster because it has faster hardware, and a clean operating system. ... As we said above, computer startup is slow because you're moving information from a slow hard drive to faster RAM
Computer running slow at startup Check out this Quick Tip
My Windows computer boots up slow
computer slow on start up Google Search

You said you tried different CPU, but it was the same motherboard, right? Maybe the motherboard speed (data bus, etc.) is just slow. Otherwise, there's not much left to try if the hard drive works OK in another computer and you've tried upgrading the memory, CPU, and power supply.

Its in your logic board controller issue, usually the problem is like that but to see what is the another problem of your External Drive is to make or use any diagnostic freeware program to identify the device where it really connected in your PC. I have also encountered like your problem but I send my External to Electronic Tech to check the power connection and controller connection going to PC. Because you said that the hard Drive is still have a normal sound then it is working then but cannot see in your Computer. Try to Diagnose first before you bring to a Technician. Good luck!

Okay the first thing you want to do is disassemble it again and make sure all your connectors are connected. Even if you damaged the keyboard cable, the computer should still boot up at least to a keyboard error screen. Make sure the RAM is seated correctly and everything is tight. It is possible that you damaged something (motherboard) as these things are extremely sensitive but hopefully you just have a loose cable somewhere.

If you need the data off the disk, a external USB case would work, or you can just get a USB adapter, without a case it may be cheaper. You can get a multiple one that will connect to IDE or SATA 3.5 or 2.5 drives for around $20 or so.

Thanks and please take a moment to rate as fixya.

you should try to remove unnecessary files in your hard drive.. afterwards, try to run the disk defragmenter. this tool will help you computer to access files faster thus making your computer load up faster..