Sound like you've stripped a gear wheel inside. There's generally a couple of gear wheels transmitting the drive from the moter to the blades. If one is going round and the other is stripped, then it will sound like it's going OK. The only way find out is to take it apart....they're quite easy. Usually a Pozidrive screwdriver is all you'll need. The screws are recessed in the side panel....remove all of them (6 or 7) and the side lifts off. You may have take off the guard if it has one, also you may have to unscrew the blades....easy!! The cable is straightforward. It lifts away when you lift the side off. You should then be able to see the state of the wheels inside. Bet you anything you like that's what's happened. Black and Decker can usually supply new wheels....they're quite good with anything like that. Put is back together the reverse way it came apart and it should be fine. Be brave.....have a go!
Denis Langley
June 2005