Reinstalled CPU and computer won't boot now....

Unplug and or remove anything not needed for the PC to post, this includes any USB connected devices. All you need is the CPU with heat sink, one stick of RAM, Monitor and a keyboard. You already said it has onboard video so use that. Double check and or reseat all your motherboard power connectors and CPU fan connector. Unplug the Main AC wall plug to the power supply and push the case power button for about 5 seconds. This drains any residual power and resets the Power supplies overload protection circuit. Now plug the AC cord back in, press the case power button and see if you can get it to POST to the BIOS.
Did you remove the motherboard from the case when you redid the CPU heat sink? If you didn't did you unplug any cables to get more room to work? If yes make sure you put them back on correctly, especially any USB or Audio header cables. If you got one of those reversed it could short something out.

alphanumeric said:

Unplug and or remove anything not needed for the PC to post, this includes any USB connected devices. All you need is the CPU with heat sink, one stick of RAM, Monitor and a keyboard. You already said it has onboard video so use that. Double check and or reseat all your motherboard power connectors and CPU fan connector. Unplug the Main AC wall plug to the power supply and push the case power button for about 5 seconds. This drains any residual power and resets the Power supplies overload protection circuit. Now plug the AC cord back in, press the case power button and see if you can get it to POST to the BIOS.
Did you remove the motherboard from the case when you redid the CPU heat sink? If you didn't did you unplug any cables to get more room to work? If yes make sure you put them back on correctly, especially any USB or Audio header cables. If you got one of those reversed it could short something out.

+1, Well said...

Also,
You did have the power turned off, disconnected, and drained when you reset the CPU, right?

Since your earlier shutdowns were almost certainly due to the CPU overheating, it is possible that the CPU is dead. They are pretty tough, but after a few overheats it is an unpleasant possibility.

jbroaf said:

alphanumeric said:

Unplug and or remove anything not needed for the PC to post, this includes any USB connected devices. All you need is the CPU with heat sink, one stick of RAM, Monitor and a keyboard. You already said it has onboard video so use that. Double check and or reseat all your motherboard power connectors and CPU fan connector. Unplug the Main AC wall plug to the power supply and push the case power button for about 5 seconds. This drains any residual power and resets the Power supplies overload protection circuit. Now plug the AC cord back in, press the case power button and see if you can get it to POST to the BIOS.
Did you remove the motherboard from the case when you redid the CPU heat sink? If you didn't did you unplug any cables to get more room to work? If yes make sure you put them back on correctly, especially any USB or Audio header cables. If you got one of those reversed it could short something out.

All great ideas good sir. I left everything as is while i was working because for the most part i had plenty of room. The only thing i took out was the RAM since it is almost right beside the damn thing. :P

I had all power unplugged but i didn't "drain" it and the battery was still in...is there a problem with that?

Also, for having everything necessary to have the computer POST to BIOS...my keyboard is wireless... so i have to have at least that USB plugged in.

Reseat the RAM, and a USB keyboard is fine. You just don't want any printers, external drives etc plugged in. You want the bare minimum components. If it still won't POST you know its one of those. If it does POST you can start adding things back one at a time until it fails again. It shouldn't be possible, but are you sure you didn't put the CPU in the wrong way? Also remove or reseat any add-in cards like sound cards. I've done CPU swaps and not removed the CMOS battery. About the only time I've ever taken one out is when I was in a no POST situation like you are. Sometimes a dead shorted out BIOS battery will cause a no POST.

Reseat the RAM, and a USB keyboard is fine. You just don't want any printers, external drives etc plugged in. You want the bare minimum components. If it still won't POST you know its one of those. If it does POST you can start adding things back one at a time until it fails again. It shouldn't be possible, but are you sure you didn't put the CPU in the wrong way? Also remove or reseat any add-in cards like sound cards. I've done CPU swaps and not removed the CMOS battery. About the only time I've ever taken one out is when I was in a no POST situation like you are. Sometimes a dead shorted out BIOS battery will cause a no POST.[/QUOTE]

I've removed the battery and tried to boot it and it was unsuccessful today...that's about all of the fiddling i want to do with it today due to lack of sleep last night. I'll still take any suggestions for possible problems...i'm willing to stick with this till I find a solution....

rchris said:

Since your earlier shutdowns were almost certainly due to the CPU overheating, it is possible that the CPU is dead. They are pretty tough, but after a few overheats it is an unpleasant possibility.

Since it started up just fine right before all of the disassembly I really do not think that the cpu is dead...and i want to try to exhaust all other options because if i have to spend a decent about to get this fixed then i'll have to wait. Can't afford to spend at the moment...

In your first post you stated.

My computer has had a bad case of the shut downs here recently so i cracked open the case and checked things... it turned out that my heat sink was loose and almost completely off of my CPU.

It could have overheated and been damaged, only way to prove it is to replace it or put it in another motherboard as a test. Did this motherboard give you the one beep when it booted up OK? If no you may want to connect a PC speaker so you can hear and BIOS beep codes. I know you will get a beep code for no RAM and even no Video if the motherboard has no onboard video. I don't know if you get a code for no processor if the socket is empty though. There are codes for a failed processor. My gut tells me to swap the power supply or test it in another PC.

In theory an overheating processor should safely shut down without damage - I've seen machines that would not even boot due to dust and overheating but still worked when cleaned, although nothing is 100% guaranteed. My money is on accidental static damage. Did the OP wear an anti-static wrist band ?

Also
"I had all power unplugged but i didn't "drain" it and the battery was still in...is there a problem with that?"

I have always read to drain power before messing inside the PC.
Myth or Reality, i can't guarantee.
I drain residual PSU power, better safe than sorry.
If it is reality, you may have fried anything...