|"why not uncheck automatically restart..."|
If you don't know how to do that, the procedure is the same as for Vista, except that to see the equivalent of Classic View in Windows 7 in Control Panel, you must set Control Panel to display Large icons, or Small icons, not Categories.
If you then get a STOP: message on a blue screen, quote the STOP error code - usually the stuff in brackets beside that on the right is useless to us.
If a problem file is named, it's usually at the end of the text - quote that if you see that.
"Ive added thermal compound to my processor and graphics card. "
If the cpu were overheating that would be obvious if you examined the current temp reported for it in the mboard's bios
The graphic card's software may or may not have some place that shows you it's video chipset's current temp. .
I have never seen or heard of thermal compound not working properly. If it was installed correctly previously, you never need to change it.
The CPU's heat sink must be installed properly so that it's sitting flat on top of the CPU.
Failing CPU fans or graphics card fans are common. Failing PS fans are generally less common - there must be obvious air being exhausted from the PS at the back of the case. They may spin too slow, or not spin at all.
"Ive also took out psu and put it in another computer, and it runs perfectly."
What make is it ?
That proves it's probably okay, but the PS working fine with another system doesn't necessarily indicate it will work fine with your system.
If you're using a graphics card installed in a mboard slot, your system should have at least the recommended minimum PS capacity ( or no more than 50 watts less than that) that is specified for the graphic card's video chipset you're using, otherwise you are likely to have problems because of the PS.