From the sounds of it, the motor's stuck. I bet simply getting in there and cleaning and relubing it will free it up. Of course, you may've burned your motor out at this point. If it's still buzzing and stinking, the motor may still be ok. People don't realize just how much the effeciency drops in a short amount of time due to dust, dirt, hair, etc. buildup. Do you have any regular fans or ceiling fans that are run all the time? Look at how much dirt and shit collects. Even cleaning a small amount has a HUGE affect on how effecient they are. Even your car cooling fans!!! That thin layer of dirt/grease does have a big affect!
People all too often forget proper and regular maintenace on their HVAC systems. Not only will proper care lengthen the life of it, but WILL save you money due to being much more effecient in the longrun.