Sometimes when a lamp blows, it takes out the low volt transformer, or low volt transformer pcb. Have you checked that? Have a look at the tracking.
It could also be a faulty cavity or Mag' thermal??
Make sure there's no hidden small fuse's on the control pcb that have blown too.
Check for power supply into the unit, and also check for continuity through the mains cable.
If everything is fine, then you might need to replace the L.V. pcb, or the control pcb.
Jon
June 2007