Question : Problem: Heat related issues?

I have a Dell Dimension 8400 that has shut itself down a few times. When starting back up I get a message saying the system was shutdown due to a heat event hit F1 to continue. My power supply appears to be running and pushing air out the back via the fan whenever I check it. It is not a strong breeze and sometimes feels like it is not pushing very much air out, but some. The airways are clean. The room this computer is located in, is kept at a reasonably cool temperature. My log files don't really tell me anything on the subject as far as I can tell. I am hesitant to purchase a new power supply, not knowing if that is really the problem. Any suggestions on how I could narrow down what the problem is, or help resolve the issue?

Answer : Problem: Heat related issues?

Open the box and clean out all dust. check the fan on the CPU heatsink is running smoothly. Remove the heatsink and very thoroughly clean it's and the CPU's surface. Use alcohol for that. Then add a very small amount of thermal transfer paste to the CPU and firmly reattach the heatsink.