Originally Posted by sbwinter2
This is the same problem I am having, but mine started with the no video and then the fan lock error came a few weeks later. I can hear the fan rev-ing faster and slower. I believe it is the power problem though and that is affecting the fan. Although I posted for some advice on this a while ago, not one person has responded. I can't be positive until I find a friend or someone who can test the power output for me (has the tools). Your problem may also be the same. There are instructions online on how to check and fix the power problem.
The fan is going to pulse the yellow wire (tach) for each revolution. If you have a scope or analog meter (not digital) you should check for this. If not, try swapping with a PC fan and see if problem is resolved. If not, you will likely have to trace it through the board - maybe look for a 0 ohm (1 black band) resistor nearby.
Of course, it's possible this is a software issue and a reset to defaults would resolve.