So, your dryer turns on but doesn't spin. You can either call a repairman out and spend $100 or more, or do it yourself with this simple, easy to follow guide. These instructions are for a Maytag/Whirlpool Dryer, but can be applied to other models as well. With a little work, you can fix the dryer belt yourself for under $20!
To verify that it is in fact the belt that is broken, remove the screws that hold on the lid and lift it. You should see the drum and a thin rubber belt surrounding it. Lift up on the belt, if it has any slack or is broken in any places it needs to be replaced. It may also have fallen to the bottom of the dryer if you don't see a belt.
You can purchase a replacement belt at any online appliance part store. Verify that you are purchasing the correct belt by comparing the model number found on the wall of the dryer behind the door. Expect to pay between $11-$14.
When your belt arrives, lay the belt along the topside of the drum with the grooves facing down. Then take the front panel of the dryer off by removing the screws holding the front panel on through the open hood of the dryer. You don't have to remove it all the way, just tilt it forward until you can slide the belt around the bottom part of the drum.
Reattach the front panel and close the hood of the dryer. Then spin the dryer around to the back and open the lower panel on the backside. This is where you will attach the belt to the pulley and motor. Loop the belt around the pulley first and then attach to the motor arm. Close the back panel of the dryer and you are done!