The microwave starts running for a few seconds then stops heating but the fan continues to run and the turntable turns.

The door switch is adjustable. one or more need adjusting to solve the problem

quite likely your microwave is trying to prevent it self from self destruct, because if the fan is not keeping the electronics components cool enough while its running the high limit thermo will disconnect power from the heating circuit, if the fan is not working it should be replaced , that's a techs job.

I’m happy to assist further over the phone at https://www.6ya.com/expert/phillip_77d32603f8052503

If microwave runs only without turn table, I am suggest to check if turntable electric motor has got short circuit. If yes, I have some left.

see this causes and fix it. God bless you
If the microwave runs for a few seconds and stops the thermostat might be defective. Watch our video on testing thermostats.
If the microwave runs for a few seconds and stops the thermoprotector may have tripped. This is a safety device to prevent the microwave from overheating. It can be tested for continuity to see if it's blown.
If the microwave runs for a few seconds and stops the high voltage transformer might have an intermittent short. This is not common. Check other components related to the microwave symptom first.
If the microwave runs for a few seconds and stops the touchpad might be at fault. This is not common. Generally speaking, if the dishwasher display is working and some of the buttons respond correctly but some don't, the problem is with the touchpad.
If the microwave runs for a few seconds and stops the touchpad and control panel might be defective. There are several other components that can cause this problem, be sure to check any other components before replacing this board.
If the microwave runs for a few seconds and stops there may be a short circuit in the main control board. Check other components first, these boards are often misdiagnosed.
If the microwave runs for a few seconds and then shuts off, a door switch might have failed intermittently. Check each of the door switches for any signs of overheating, arcing, or burning. Also check each of them for continuity. Replace any of the switches that is visibly damaged or that only has continuity intermittently.

The high pitch sound to me may be coming from the speaker on the main circuit board. Try to unplug for a few minutes, reset clock time and then try again. If same issue, may need new PC board. When you say Microwave continues to run are you meaning the Turntable is turning and the fan running?? Or is it just timing down. Almost never does it actually keep heating. On GE units I mostly find bad door switches will cause a back feed and make the tray turn and the cooling fan for the mag to run. To see if that is the problem You have to look at the door switches behind the front panel on the left side and see if any of them have any browned connections on the terminals where they push ontl the back of the switch. That will cause the fan and turntable toi run, but wouldnt cause a high pitch squeal. These companies use switches wtih small 3/16 terminals that dont give a good enough grab on the switch, they get loose and hot and make the switch go bad. I replace that switch with a switch with 1/4 inch terminals and runa short section of Hi temp wite to it and it wont go bad again. Just cheaply made!! Also I guess the squeal could come from the turntable motor area. So By fixing the switch problem it could fix your squeal. With nothing else running you may be able to hear motor and coupling noise you couldnt hear before.

With the model number, we can offer more specific advice or an estimate.

But since FixYa does not notify us of follow-ups, you will need to post a new help request.

Assuming you already ruled out the exhaust fan there are 2 stirrer motors, one for the turntable and one for the stirrer blades in the top. One of those could be bad. eric

Sounds like a classic bad door switch or switch holder. If you or a friend decide to work on it, we have *critical* safety info, info on door switch testing and replacement, and oven disassembly info at our site, which is linked at our listing here on FixYa: http://tinyurl.com/yzjozk You can find helpful exploded view diagrams and order parts by entering your base model number (without the suffix) here: http://tinyurl.com/gv383

This is not safe. If the fan is not running, the magnetron will quickly overheat and be destroyed. We answered this in more depth in the other place you asked it.