What CPU are you running?
What motherobard are you using?
What BIOS version?
From my experience with using AOD on some AM3 and FM1 chips, it's not accurate. It takes the temperature reading...below the socket or something.
Use CPU-Z, HWMonitor, or AIDA64 to monitor your CPU frequency and temperature.
You can also try using your motherboard manufacturer's software (if they have any).
Erm...do you have any power saving features on? Cool N' Quiet? etc? These fill reduce the clock frequency when the system is idle to save power.
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