Random Hangs, no idea whats happening

so in the past 3 days my computer has started randomly hanging, complete lock up.  Nothing responds, not even numlock/capslock/scroll lock lights on the keyboard will go on or off, and there is often looping sound.  This hang continues until i manually turn off the computer.

ive run seagates app to test my hdd's, and they passed all the tests.  Ive run memtest, and my ram is fine. ive checked the temperatures for video card, mobo, cpu's etc, and they are all within acceptable limits.

i've reinstalled and reformatted 3 times, first time i reinstalled vista, then reformatted and installed xp and the same thing happened, so i zero filled the drive to makes sure that it wasnt some kind of weird lingering software issue and then put vista back on.  I added another to put more air over my cpu/chipset/ram and the system ran fine for over an hour last night, but then after being up for about 30 mins today, it hung again.  After rebooting fromt he hang it hung again about 2 mins after boot, and has now been going for about 20 mins.

any ideas wtf is going on?  any diagnostics i should run?


Also:
Core 2 Duo e6300
Gigabyte 965P-DS3 (rev. 3.3)
2 Gb OCZ Gold pc6400 ddr2
Nvidia 7900 GS
Seagate 500 gb hdd (only a few days old)
OCZ Gamestream 700w PSU
3 120mm fans, plus a 90mm side fan.


tl;dr    compy is fucked, help ploz.

OP is back!

my compy is fucked again, this is driving me crazy.

im going to switch out the psu probably tomorrow, and try to borrow a video card from someone to test that out too.

if that doesnt work, i'll just become an hero.