Hey Arthur,
This might suprise you, but it doesn't sound like your Power Supply Unit at all, altough it could be a contributing factor. If you put your hand near to the vent, is the fan still blowing out air?
It actually sounds like your whole system is too hot. Looking at your PC spec's, I see you have a fanless 6600 Geforce? You have to be kidding me? Is there no cooling for this card at all? These cards will automatically shut the PC down when they reach their temperature thresholds. This would explain why you were not immediately able to start your PC for a while until your GPU had cooled down.
Download speedfan, which will give you an idea of all your system temperatures:
SpeedFan - Access temperature sensor in your computer
If you ever smell burning, please don't keep your PC running. I'm suprised it is still working at all. If you just have a heatsink on your graphics card, then your PC needs to be very very cool. This means as well as your
PSU having it's own cooling. There should really be a fan at the back of the PC to blow out the hot air, and a fan at the front of the PC to bring in the cool air. Airflow inside the PC is important, so keep those cables out of the way, and make sure that all remaining vents and heatsinks inside the PC are free of dust.