Q-fan on Asus M2N-SLI Deluxe won't work

[codertux]

Hello, I'm having trouble with Q-fan on my motherboard. It used to work fine, but after I've unplugged the CPU fan while the computer was running (just to see how hot the CPU gets without a fan) it stopped working. Now the fan works at full speed all the time, no matter what I choose in the BIOS. I've also tried enabling Q-fan in Asus PC Probe but that didn't work either.
The fan is a Thermaltake Smart Case Fan (120mm).
If I connect it to a chassis fan header, Q-fan works perfectly.

What can I do to get it working again on the CPU fan header?

[Hemi]

if you have a fan boost function make shure it is disabled. reset bios is the only other thing i can think of. good luck

[codertux]

I have tried that, and also another bios version... same thing. Now I have an AC Freezer64 PRO PWM and it works perfectly...