mine has done the same twice now(quite old) on mine it was the brushes in the main motor.
disconnect from mains,take back off, stand away and start it up again,have a look...mine flashes,spits and farts and does not sound healthy.
brushes dead easy to replace, slot in type normally,mines on it's third set,replaced twice myself.
but Unplug from mains before doing anything please!!!!
Andyshrops, July 2008