Just a few days ago when my car was turned off a fan started running inside (might have been while the car was running, couldn't hear it then). Now the battery keeps getting drained to the point where nothing will turn on (lights, power locks, etc). Whenever I hook up jumper cables the fan starts again. After jumping it the car will run fine, but when I turn it off the fan continues to run and drains the battery again. Any idea how to solve this problem?

 

In the fuse panel under the hood, there should be a fan control relay. Swap that with a known good relay (they're all the same!) and see if the "always on" issue follows that relay. If it does, than you know you've got an easy fix.

If there is no relay for the fan, then you have an issue with your BCM, and may need to reset the computer (even though the battery is dead, there is still SOME juice to keep the settings in the main computer).