Our microwave oven will not cook or reheat at all. The lights, clock, etc. all work. Is this also the magnetron leaking? Is this expensive to repair and can you do it yourself?

it has a fuse located behind the main control panel. you will see it after you remove the cover

The magnetron is shorted or the inverter board is defective if microwave is 7 years old or less.

There are a few things that will cause this problem, the high voltage diode, or the high voltage capacitor, and the magnetron are usually the culprits. I find that one or more of these parts will go making the cost to repair at least $100.00 and up.

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

Tat would be a magnetron problem. The magnetron is what provides the heat

magnetron is leaking internally, do not use until magnetron is replaced. the mag creates interference with the control board and resets it

Test the high voltage capacitor, the rectifier diode.or the magnetron.

The diode and capacitors can br tested. The capacitor must be allowed discharge before testing, or you risk to get electrocuted, even if power is off. Capacitors can get discharged by shorting their two contacts.
Replace the magnetron if the checks and all of the high voltage component tests are good, but the unit still does not heat.

All locations, and description of this parts can be located using the diagram here: Counter top.

Parts must be tested to find out what is wrong.

Remember that microwaves are potentially dangerous devices if not repaired properly, the job must be done by a competent person.
A microwave energy leakage test must always be performed when the oven is serviced for any reason.

Regarding parts, contact the seller here to purchase parts.

Your magnetron is leaking and needs to be replaced.

Are you saying that the oven seems to shut off while cooking? Does it also happen if you cook at full power? This may be a bad connection on the controller (which we repair) or a failing magnetron. Please give usd a little more detail so we can follow up.