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.
FX-8350 @ 4.8GHz // ASUS Crosshair V Formula 990FX // Sapphire Vapor-X HD 7970 + Dual-X HD 7970 // Thermaltake Frio w/ push-pull (using Antec Formula 7 Nano-Diamond + Cooler Master JetFlo fans) // 8GB (2 X 4GB) G.Skill RipJawsX 2133MHz // Corsair TX850 850W // Corsair Force GT 120GB SSD (OS) // Kingston V200+ 120GB SSD // WD Caviar Black 1TB // Windows 7 Ult x64