If it is the belt that drives the fan, look at the back of the dryer.
There is a plastic cover about 30cms long and about 5cm wide with 2 screws holding it on running from the top left on a 45 degree angle to the centre of the dryer.
Take this cover off and simply slip the belt back on over the pulleys.
Should take you 5 mins, I'd recommend getting a new one while you've pulled it out or off the wall because after time they slip off and will continue to do so until you get a new non-stretched belt.
Antho, October 2009
