If it has a UK fused plug the first and easiest thing to do is to check the fuse.
Then you should try and ascertain whether it's an electrical or a mechanical fault. Does the red lever have exactly the same feel to it as it always did? If not, then there's probably a bit of broken plastic beneath the lever which actuates the actual switch.
Did the motor sound as if it was labouring when it was last working? If so (or even if not) there may be a thermal fuse somewhere inside, most likely attached to the motor, to prevent it burning out if it overheats. If you can take it apart it should be possible to follow the wiring through from the plug, through the switch, to the motor and hence back to the plug. With a test meter it's possible to check for any breaks in the circuit.
But it could be a problem with the carbon brushes in the motor - see https://therestartproject.org/wiki/Electric_motors#DC_and_Universal_.28AC.2FDC.29_Motors