I upgraded to Athlon Dual Core 5050B processors on 4 Dell e521 desktops. I am using these with Server 2008. Only 1 of the computers has this problem.

Sometimes on startup (not every time) the processor fan will accelerate to its max speed and stay there forever.

With the fan racing CoreTemp reads 23C.
When the computer happens to start without the fan racing CoreTemp reads 38C. If I use SuperPi to load the system to 100% Coretemp goes up to 43C. The fan does not accelerate when the processor reads 100% load.

I carefully followed best practices when installing good thermal paste with the stock heatsinks on all 4 units. I have cleaned and started over with the problem computer but nothing changed.