strange recurring black screen of death crashes...

[Xhiggy]

I've had a hard time diagnosing this so hopefully someone here will have some ideas.

Recently built this computer - for a couple weeks now have had recurring computer crashes (black screen, no signal to the monitor, keyboard unresponsive, reset button won't work). After the computer crashes, the computer's fans (or one fan) becomes really loud.

This problem has occurred in both Vista and Linux, so I'm pretty sure it's a hardware thing.

Processor: Intel Q6600
Motherboard: MSI P6N SLI Platinum LGA 775 NVIDIA
Memory: Patriot eXtreme Performance 4GB(2 x 2GB) DDR2 SDRAM DDR2 800 (PC2 6400)
Harddrive: SAMSUNG SpinPoint T Series HD501LJ 500GB 7200 RPM SATA
Optical Drive: Pioneer Black E-IDE/ ATAPI DVD Burner
Power Supply: CORSAIR CMPSU-520HX ATX12V v2.2
Video Card: EVGA 256-P2-N765-AR GeForce 8600GTS 256MB 128-bit GDDR3

At first it seemed that maybe the memory was the problem, and just today I replaced it with some Crucial memory, which according to their website, is "guarenteed" compatible with my motherboard. it passed memtest, but the computer still crashed.

I've noticed a possible recurring pattern...it seems my computer will crash about 10-15 minutes after I first turn it on that day. Then after it crashes and I hold the power button to shut it down..when I then turn it on again a minute or so later, it them seems more stable (doesn't crash at all).

Any ideas on what the problem is would be greatly appreciated.