yay!

my system keeps on crashing but it looks like we can stop shooting in the dark.

I've deactivated the Windows reboot option to force the PC to crash instead of rebooting.
And finally I've had the mighty BSOD (Blue Screen of Death).

Attempt to reset the display driver and recover from timeout failed.

*** STOP: 0x00000116 (0x86E7C510, 0x8E501E80, 0x00000000, 0x00000002)

*** nvlddmkm.sys - Address 8E501E80 base at 8E4F6000, DateStamp 48ebd52f
my GFX Card:

XFX GF8800GTX XXX
NVIDIA GeForce 8800 GTX, 768 MB,
384 Bit, PCIe x16
I've updated my gfx-drivers - let's see if that fixes the problem.
if not, I'll try to get a new power supply and if that doesn't work I'll change the gfx card.