I have a two year old desktop, some random quad core HP desktop.

It used to run very quietly, but in the past month, the fans start up anytime anything "serious" is being done -- compiles, playing video, etc.

Right now, speedfan and speccy report the cores are between 50C and 70C. Speedfan reports this as hot. (Nice flame icon.)

Well, the system does sit on my carpet, so two weeks ago, I took off the lid, and cough *cough* it was pretty filled with dust. I got out an air can, turned on a vacuum and carefully got out all the dust that I saw on

• the CPU fan
• the case fans
• any fan I saw (graphics board)
• and blew out all the dust I could from all the circuit boards.

And then I closed the case back up. It has definitely run cooler since then, but it still runs hot, and I hear high speed fan noise I never heard before.

How hot is too hot? At what temps do consumer grade CPUs die?

What should I be looking to do?

• Replace CPU fan? (It seems to work)
• Replace power supply fan?

Assuming the dust problem is gone, where should I be looking to determine why the machine is heating up?

Epilogue: After following the various pieces of advice given here, the system did run cooler, but it was still noticeably running louder (hotter) than just a few months prior. I ended up purchasing a new cpu heatsink and fan and during installation found the cooling grease from the original heatsink was just a dried, cracked layer, probably more of an insulator than heat transfer agent. With the new fan AND the new heatsink compound, the system ran much much cooler and the fan rarely turns on.