Check the filter is clean, if it is an old filter best buy a new one, the motor is temperature tripping due to overheating caused by a blocked filter.
Before buying a filter, remove it and run machine, if it fails to cut out then the filter is the most likely cause, if it does stop again, the machine may be stopping due to the motor overheating as it starts to fail, most likely cause, worn brushes/commutator.
Rob, October 2009
