You checked the obvious.
Nothing works, the only way to get that pesky fan to stop is to shut the power off.
Well, if you are going to have a problem with your HVAC equipment, this is the one to have. The heating and air conditioning still works fine. If you have allergies your fan should be running all of time anyway to filter the air more. It really doesn't hurt the motor running all of time. And it usually isn't an expensive repair.