Hi, it could be mighty dangerous to turn the Fan OFF!
Get Temperature Monitor to see if it's heat related...
Please report the highest temps.
It is always on at default speed when the Mac Mini is on to prevent overheating. The only time it is off, is when the Mac Mini is sleeping or shut down.
If it is running at high speed, then > Resetting the System Management Controller should help unless you have a disconnected or broken temperature sensor.
1. Shut down the computer.
2. Unplug the computer's power cord.
3. Wait fifteen seconds.
4. Attach the computer's power cord.
5. Wait five seconds, then press the power button to turn on the computer.
Message was edited by: den.thed
Adding for clarification that a Early 2009 Mac Mini only came with a 2.0GHz or Configure to Order 2.26GHz Processor Upgrade.