I have the same problem. Here's how to take the lower unit apart:
1. Tak eoff the cover for the light
2. Undo the two screws
3. Take out the light bulb (press in an rotate)
4. Pry the top off with a flat head screw driver; insert the blade where on each side; there are instructions right on the unit
Chances are your belt is broken. I will need to find a new one; you can always order one from sears.com.
Martin
Martin Schedlbauer, June 2006