HI, magnetron, or most probably the invertor has failed, if less than 3 years old its under warranty, contact me for info microwave-repairs.co.uk
kindest regards
Oh and just for good measure the gypsies warning, it is deadly true, so take care
Whatever happens please remember you are messing around in a piece of equipment that runs at 4000volts and due to the design of its circuitry under certain fault conditions it remains lethal months after having been disconnected from the mains supply. its not rocket science as they say, but it is not for the layman either. Contact me via microwave-repairs.co.uk if you need further help.
patrick
August 2010