The microwave turns on when the door is opened

The switch assembly is somehow staying "closed" satisfying the interlock and enabling it to run.
Disassemble the unit, beware specially of the high voltage capacitor, if you aren't comfortable or competent, buy a new microwave. If you are mechanically inclined, disassemble the unit until the switch assembly is accessible; it will have the door latch attached to it.
The switch is either broken or something? exogenous is keeping it closed. It may have come loose due to the door slamming?.
It's a simple fix. I am certainl you will be successful.

There is an power interlock inside the oven that breaks the power connection to the magnetron when the door is open. Most likely, something is stopping the switch from opening.

Check for a small plastic probe on the door that may have broken off inside the oven keeping the circuit made. Otherwise, open the oven and see is some foreign object is keeping the connection made or if the interlock needs to be cleaned out so it can function.

It sounds to me that your door switches aren't working.Your oven is protected by a couple of switches that engage when you open or close the door.They control a couple of safety features and also your interior light.One of them seems defective.

It is very dangerous, you're filling the room with radiation, may be best to just dump that one, unless you are a little bit competant with mechanical stuff, in which case it's probably the sensor on the door not registering that it is open,. might be a physical thing, i.e. moved a little. or maybe a electronic thing, requiring a new sensor itself.

We are very sorry to hear this and we apologize for the inconvenience this has caused you. We would be glad to look into this if you could email us at [email protected] with your name, address, phone number and the model & serial numbers of the Microwave.

Check door interlock switches and moisture on the control panel causing errors.

this is dangerous; replace or adjust your door switches the interlock switches should only allow you to turn on the microwave when the door is closed

Check those three microswitches in the latch assembly.

This is usually caused by either a bad door switch, a loose door switch mount, or a problem on the control panel.

Even though a door switch clicks, it may still be bad inside.

Door switches are most often damaged by opening the door while it's cooking (instead of pressing Stop / Clear first) or food
/ grease debris in the switch.

If you or a friend decide to look into it, we have critical information on safety, disassembly and door switches at our site, linked here on Fixya: http://tinyurl.com/yzjozk

If the top is open, the upper door switch should be open and the high voltage section should not be energized. That's the way it's *supposed* to work. But that buzzing is worrysome! Does the turntable turn during this condition? Does the inside light come on? How about the fan? If not, then I would doubt that it's cooking. If so, some models will do this. It's not uncommon to notice that the fan and light will try to come on for a split second when you shut the door. This would not indicate a problem. It has to do with the timing of the door switches and a replay on the board. If it's still under full warranty, it wouldn't hurt to call a GE-authorized servicer.