New build, CPU posts then dies

[Erock26]

I transplanted all new components for in my old AMD 2800 (not sure if the change to intel matters).
New:
Motherboard: EVGA 122-CK-NF67-T1 LGA 775 NVIDIA nForce 680i LT SLI ATX Intel
Video Card: POWERCOLOR X1950PRO512MBAC Radeon X1950PRO 512MB 256-bit GDDR3 PCI Express x16 CrossFire Supported
Processor: Intel Core 2 Quad Q6600 Kentsfield 2.4GHz LGA 775 Quad-Core Processor Model BX80562Q6600
Ram: CORSAIR XMS2 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory
500 W antec power supply

First time it turned on, it booted all the way to windows and then turned off. Since, I've been able to get it to POST but it shuts down shortly there after. Occassionaly I can get into BIOS but it'll shut down before I have a chance to look at anything. I've been thinking it may be a power problem, but would the video card and processor really need more than 500W? Or if it's a heat problem and all of the fans are working, how do I fix that? Can the processor really heat up enough in 15-20 seconds to the point that it would have to shut down?

-Erock

[Erock26]

One more thing, the computer turns off in a progressively faster fashion. I timed my last turn on lasted 26 seconds and then I turned it on a few seconds after that and it only stayed on for about 15 seconds. This makes me think heat once again but i've taken out the processor and wiped it clean with a rag, reseated it with spread silver and dabbed silver on top for the sink, but neither worked. What do I do??!?!?

[poeg]

Check chipset heatsink with digital thermometer match to mainboard health section's reading. A few degrees is OK anything larger is poor contact.