Seems Like a dying PSU to me?Setek what is the 12V rating of the pSU?
The PSU that was in there has 36A on the +12V I would have to pull down the machine to see what is running on the one inside it now.
Machine restarts or shuts down (usually shuts down) whenever anything graphics intensive starts. My machine will be on hours and is quite fine until I start running a game and it may still be fine until something graphics intensive occurs and it just goes. My specs are in my sig if anyone wants to know to query I have a generic PSU but its been running the same card fine for hhhmm perhaps almost a year now give or take.
Something getting hot when you go into high video mode is what it sounds like.
What is your cooling like?
Stock cooling but now that you mentioned that I had lost the ability to control my fan speed from the Catalyst for a while now I thought it was just a driver issue but it could be that the fan is gone.