Did changing out the needle work? Here is some info I put together for when a machine won't stitch:
http://www.quiltingboard.com/vintage...g-t182255.html
I just bought one of those - kind of a cool machine. I can see how you might have problems with that belt. Some people turn those into treadle machines. Under where your cord is setting in the front, is a little plastic part that can be unscrewed to remove it - a treadle belt runs through there and a chanel in the back - look behind the machine and under you will see a hole where the treadle belt can come out. This machine should fit right into a Singer 66 treadle base.