Dryer Issues

My dryer had stopped working, the motor will run but the drum would not turn. I opened it up and saw that the belt was lose but not broken it had come off the pulley and the spring was dangling lose. I reset the belt and re-hooked the spring. the dryer seemed to work again. I then put towels in the dryer and it would not turn again so I took a few out and left 4 in there, it will turn but does not seem like its turning like it should. Is this a sign of a bad belt that needs to be replaced or is it something else?