Computer won't reboot after overheat..HELP!

Hey all, I'm new to this site so hopefully I won't irritate anyone by asking this questions. Here's the sequence of events:

1) Intel Active Monitor warns me system zone 2 is overheating (on my motherboard this is near the heatsink)
2) I up the threshhold two degrees...a few minutes later, the system shuts down
3) I try to reboot and though the computer turns on...nothing happens, no BIOS, no windows startup, etc...computer then shuts down again.
4) I took out the heatsink, reinstalled...gave the comp a break and now power isn't even running through so NOTHING is happening. I've tried a different cable, different outlet, etc...

My question: Does anyone know if my Mobo is dead, CPU is fried, or do I simply need a better power supply...I have a powmax 400W case.

THANKS IN ADVANCE

Specs:
Intel D865PERL board
P4 3.06Gz
1G DDR333 Ram
ATI Radeon 9600
120GB Caviar Hard Drive
40GB Western Digital Hard Drive