Hi Queenii, the cause of a complete failure in most microwave ovens is the machines deliberate blowing of its internal monitor fuse. Now a fuse is designed to blow when the conditions it is monitoring reach a point that could be harmful to you or itself. Fuses do not blow usually without good reason, so you need to ascertain why ? Best not to mess about with a machine that runs at four thousand volts and is capable of lethal shock even when unplugged !!!! Best to call an engineer or take it into a local specialist. If they are any good they will have a relatively small inspection fee.
My contact details are on microwave-repairs.co.uk
kindest regards
patrick
June 2009