I am not sure what you mean by "It sounds like everything is working"?
So am assuming that you can hear the motor running (not buzzing) and the drum does not turn.
Try rotating the drum in the correct direction. It should turn fairly easily.
If drum rotation is OK then odds are you have the belt on wrong.
There are belt diagrams at the start of this section.
Make sure that the ribs on the belt face the motor's pulley and the outside of the drum.
If they do not also be sure to check the belt before putting it back together.
If the motor pulley has been running and slipping on the belt there is a good chance that it has ruined the belt at that location.
Check that the idler/tension pulley is putting tension on the belt.