I was heating my dinner when the mircowave just stopped cooking. The light remains on all the time but no cooking occurs. The clock and timer still funtion. Any ideas?

motor or circuit board failure

The first thing I would suggest is a hard reset. Unplug the unit for a minute or so. Then plug it back in, set the clock and try again.

If that doesn't work, leave it unplugged for about 5 minutes.

Possible fault with your timer controller unit processor board. In many cases insects can cause secretion and so the clock circuit can malfunction. remove the unit and use a air cleaning. heat the board if there is presence of moisture.

probably a defective magnetron; very common for this vintage microwave. there are usually generic magnetrons available; as the original GE part will be expensive.

you need to buy a new one because it is broken.

IT COULD BE A NUMBER OF THINGS RANGING FROM DIODES TO CAPACITORS TO YOUR MAGNATRON OR THERMOSTAST OR TRANSFORMERS. IT'S DIFFICULT TO DIAGNOSE WITHOUT SEEING THIS MICROWAVE. YOU MAY BE BETTER OFF GETTING YOURSELF A DIFFERENT ONE.

Pressing "timer/clock" button 4 times turns on and off demo mode.

Disclaimer: I'm a DIYer, not a technician.

Our GE over-the-range microwave stopped producing heat yesterday while warming part of the T-giving feast. Everything else (fan, control panel, light) works fine.

After disassembly and testing last night, I discovered a defective "secondary door switch." Your Kenmore uses a similar switch (~$19 on-line), and that might be the problem. But it also could be other things, such as a bad thermal cut-out.

If you know anyone who's handy with a multimeter, most of the basic diagnostics seem to be pretty straightforward.

One of your door interlock switches is defective . I would suggest having it repaired by a qualified repair tech in your area.