Kenwood KEN GT/AL17 does everything except cook?

I was given my Kenwood KEN GT/AL17 microwave by a friend who had an extra one about five years ago. The light was already blown and it was beginning to show signs of wear and tear, but worked perfectly. A few weeks ago, just after Christmas, my daughter told me that her oatmeal wasn't getting hot. The timer works, the turntable works, everything works except the part that makes the food get hot. Is this fixable, or do I have to get a new microwave?