Check why the belt has come off - if the bearings have failed the drum pulley will be running off the vertical and will throw the belt off. Check for bearing failure by seeing if there is any vertical movement between the moving stainless drum and the fixed outer drum. There should be no vertical movement between them - if there is the bearings have failed and will soon collapse.
If theres no problem with the bearings, Slacken or remove the motor mounting bolts, which should give enough play to replace the belt. Refit or tighten the bolts and the belt should be correctly tensioned.
Repair and service your own washing machine. Go to www.2ndwave.co.uk/manual.html
dannyboy
February 2009
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Try fixfault.com to fix washing machines.