Hello everyone! I have the similar problem. I have a Dell Dimension, 3000 with 3ghz Pentium 4 CPU with 1gb RAM, added geforce PCI ATI Radeon 256 mb video card, added sony dvd burner.
1st I bought the pc, it was in little cabinet with door open, I used it for a year, but some gusest isn the house (or my kids, or cleaning lady) left the cabinet door opened probably only once or twice the whole time. Nothing bad happened, but I had to shuit it down(cause both fans were running like crazy).
Months later I started self shut downs. My wife actually wrote down the message "Previously shut down due to thermal event". My video card's fan is maing a lot of noise too. I opened the case, and checked for dust for the first time, It was horribly dusty!!! I vacuumed, cleaned it very well. Even ordered the best thermal paste and reapplied it(don't remember the brand). Both fans seem to be working just fine.
here is the problem. Pc turns on, everything seems great, all applications are working, PC shots down, or screen crashes after 5-20 minutes.
What are the problem possibilities?
1) Did I fry the motherboard? (if I did, wouldn't it start?)
2) Video card fan might be problem?
3) Fans seem to be working, how can I check their speed?
4) Should I clean the heat sink, and reapply the paste? ( i did it 2wice!)
5) Did I overload the regular Dell pc too much with video card and 2 gb ram? (It worked fine for the longest time though)
Please help, I can't afford a new pc yet....