First off a microwave is a machine able to kill or injure even when unplugged, too long a story to go into but don't say you were not warned, if you don't know, don't go. the most common cause is down to the safety interlock switches being faulty, just as likely on this model though is the magnetron is at fault. not a job for the untrained. if i can help further I will, contact me via details on microwave-repairs.co.uk
patrick, April 2012