Random Shut Downs

[iKettles]

A friend of mine is having problems with his system. Specs are as follows -
Athlon XP 2600+ Socket A (not sure)
Asus A7V8X
512mb RAM
PNY GeForce 6600GT AGP
He's been having random shut downs for a while now. Just generally browsing and it will go, particularly when watching videos/playing games. I bought him a new PSU but things are still the same. Running ATiTool with the furry cube it artifacts badly however there's no shutdown. Orthos Small FFT's and Blend doesn't cause a shut down either. Any idea what could be going on?

 

[iKettles]

Gave it a good clean, it's the fact that it can last Orthos Blend and Small FFT's without crashing. Whether it be idle or load it still shuts down.