When tumble dryer is switched on the drum doesnt turn. The belt has shredded but not completely. You can turn the drum by hand. Im not sure what has caused the belt to shred or if it is anything else wrong with it.

Sounds like a broken belt to the drum.Check that first. Make sure the drum will turn by hand and not seized up. Check maybe the belt has come off the motor.

Nothing works or drum fails to turn (tumble dryers)
Ensure that the power supply to the dryer is switched on, the timer is set to the desired drying time and the door is correctly closed. If you have a condenser model, also check that the bottle is empty and is fully pushed into the machine.
http://www.whiteknightrange.co.uk/whiteknight/faq.html

The first thing to establish when troubleshooting the clothes dryer is whether the dryer will start or not. If it won't, start by checking the outlet and the circuit breaker. Is the dryer plugged in or has it tripped the circuit breaker? If the breaker has been tripped, flip it back on and try the dryer again. The drum should turn without a problem.
If both plug and breaker are fine, you'll need to inspect the door switch as you continue to troubleshoot the tumble dryer. When you close the door on the dryer, a plastic peg should click and operate the switch which allows the dryer to work. The peg might be bent or broken, in which case it won't connect with the switch. You can try to straighten the peg, but if it's broken, you'll need to replace it. If the peg is fine, the switch has probably failed and will need to be replaced.
http://www.doityourself.com/stry/troubleshooting-a-clothes-dryer-drum-doesnt-tumble#b#ixzz3FOOQgtAT

Good luck!

check the belt that goes around the drum to be correctly mounted at the motor area also inspect the rollers that hold and turn the drum

Belt has jammed or drum has slipped out off drum guides

could be any of these,, check here http://www.partselect.com/dryer+dryer-wont-heat+repair.htm, also http://www.partselect.com/dryer+dryer-wont-tumble+repair.htm

the belt is broken

It won't tumble If your dryer doesn't tumble, check these: Belt Motor Door switch Belt Dryers have a drive belt that turns the clothes drum. If the belt breaks, the drum stops rotating. Then you need to replace the belt, and often the idler pulley, because the pulley tends to wear out at the same time. Click here for a belt installation diagram Motor If the dryer motor only hums when you press the Start button, the motor may be burned out. Here's how to test the dryer motor: Remove the belt. Check for obstructions in the blower fan housing. Manually rotate the shaft of the motor. If the motor is very stiff, or impossible to rotate manually, and the blower fan housing is clear, you need to replace the motor. If the motor rotates freely, run the motor momentarily with the belt removed and the blower in place. If the motor runs fine with the belt removed, there may be a problem with the idler pulley or the clothes drum. Try to rotate the drum by hand. If it is very difficult to move, correct any problem with the rollers or pulley, and then reassemble the dryer and try it again. If the motor hums but doesn't rotate on its own even with the belt removed--yet you can turn it freely by hand--you usually need to replace the motor or the motor start capacitor. Door switch Your dryer can't operate at all if the door switch is defective. It's inside the dryer main housing near the door frame. Sometimes you need to raise or open the top or front of the dryer to reach the switch. If it's defective, you need to replace it.

If dryer does not spin it is usually a problem with the belt or the motor. Check also door switch.

See also following indications from Repairclinic:

It won't tumble If your dryer doesn't tumble, check these:

Belt
Motor
Door switch
Belt Dryers have a drive belt that turns the clothes drum. If the belt breaks, the drum stops rotating. Then you need to replace the belt, and often the idler pulley, because the pulley tends to wear out at the same time.

Click here for a belt installation diagram.

Motor If the dryer motor only hums when you press the Start button, the motor may be burned out. Here's how to test the dryer motor:

• Remove the belt.



• Check for obstructions in the blower fan housing.



• Manually rotate the shaft of the motor.

If the motor is very stiff, or impossible to rotate manually, and the blower fan housing is clear, you need to replace the motor.

If the motor rotates freely, run the motor momentarily with the belt removed and the blower in place. If the motor runs fine with the belt removed, there may be a problem with the idler pulley or the clothes drum. Try to rotate the drum by hand. If it is very difficult to move, correct any problem with the rollers or pulley, and then reassemble the dryer and try it again.

If the motor hums but doesn't rotate on its own even with the belt removed--yet you can turn it freely by hand--you usually need to replace the motor or the motor start capacitor.

Door switch Your dryer can't operate at all if the door switch is defective. It's inside the dryer main housing near the door frame. Sometimes you need to raise or open the top or front of the dryer to reach the switch. If it's defective, you need to replace it.

Dryers have a drive belt that turns the clothes drum. If the belt breaks, the drum stops rotating. Then you need to replace the belt, and often the idler pulley, because the pulley tends to wear out at the same time.

Click here for a belt installation diagram.

Motor If the dryer motor only hums when you press the Start button, the motor may be burned out. Here's how to test the dryer motor:

• Remove the belt.
  
  
• Check for obstructions in the blower fan housing.
  
  
• Manually rotate the shaft of the motor.
  
  

If the motor is very stiff, or impossible to rotate manually, and the blower fan housing is clear, you need to replace the motor.

If the motor rotates freely, run the motor momentarily with the belt removed and the blower in place. If the motor runs fine with the belt removed, there may be a problem with the idler pulley or the clothes drum. Try to rotate the drum by hand. If it is very difficult to move, correct any problem with the rollers or pulley, and then reassemble the dryer and try it again.

If the motor hums but doesn't rotate on its own even with the belt removed--yet you can turn it freely by hand--you usually need to replace the motor or the motor start capacitor.

Door switch Your dryer can't operate at all if the door switch is defective. It's inside the dryer main housing near the door frame. Sometimes you need to raise or open the top or front of the dryer to reach the switch. If it's defective, you need to replace it.

if this helps please vote me a fix ya

has the belt shredded and wrapped itself around the shaft? try to manually rotate the drum to see if the belt is free and the motor shaft moves. it sounds like the motor is stuck and the smell is the uncirculated heat at the back. let me know your results.
taking the lid off will gain access.