My dell Dimension 8400 is working fine unless I shut it down and let it cool down. After an 1 hour or so it will not boot. It beeps a bit and if I insist on restarting it, it will blow the fan like a vacuum cleaner. If I keep trying by holding the start button and restarting, I can eventually get it to boot up after which it runs fine -- so far for days --
I am scared that these symptoms are the beginning of the end for this machine.
I have cleaned the machine (it was very dusty) and it seems to work like normal -- All fans are functional.
I reseated the RAM but did not retest the cool-down no boot problem for fear that I would not get it to start at all.
Either one of your sticks of RAM is bad, you've just about burned your cpu up, or your power supply could be failing due to heat and dust. I'd try replacing the power supply first (or at least testing another one in your computer first if you have an extra).