Dryer turns off

My son was having problems with our dryer while I was out of town. He said the drum wouldn’t turn, but he would turn it manually, and once it would get going, it would continue. He said if he would open the dryer door, the heating element would stay on. I wondered if there was something going on with the belt. I bought a kit and replaced the 2 rollers, the idler pulley unit, and the belt. The new rollers and pulley move much more freely than the old ones. Now the dryer will start and run on all three settings - light, medium, and heavy - but it turns off after 4 or 5 seconds and smells really hot. Any suggestions?