I learned how to sew on my Mom's Pfaff 230. The only thing I can add is that the foot control isn't the original. That machine came with a cool, round foot control. It might be worth sliding off the bottom of the foot control to check the connections inside.
I also wonder if the belt may have been a little dried out, and maybe softened up as you were working with it. That might explain why you could hear it spinning but the machine wasn't moving.
It's a great machine!