The microwave door seems to be loose. The door will remain shut, but the light is on in the microwave and it won't run until I push upwards on the door. How can I tighten the door hinge?

BEFORE DOING ANYTHING DISCONNECT OVEN FROM POWER. I do NOT recommend doing repair by yourself, if you NOT are really very familiar with electric repair, or have at least basic training in electric device repair and maintenance.
"When door is opened display goes dark. When door shuts display lights all characters and then says "touch clock"."
Obviously, by opening door, oven gets disconnected form power line.
This is mostly caused by loose connections on wiring socket, and can be anywhere inside. Check security micro switch on door latch. This switch normally disables only running the oven when door is open, for security reasons. In your case, it seems that opening door disconnects oven from input power. Sometimes the switch is loose, or wires are not firmly pushed in the socket. If the power line wiring is loose, and by opening door looses contact with socket, it can touch metal housing inside, cause short, electric shock, serious even mortal injury and fire. This is dangerous high voltage switch, and to access it one must open oven from the back and take off the cover. I do not recommend doing it by your self.
Rem: Replacement micro switch is couple dollars.

There are a couple of microwave ovens out there where after it has finished cooking, the light and fan continue to run until you open the door. Then the fans shuts off, but the light remains on. When you close the door, then the light shuts off. If the light and fan go back on when you close the door, then you have a bad door switch.

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My microwave will not heat up its in a defrost mode. How do I change it?

I had the same problem with the fan not wanting to shut off after the repair. Once I set the clock though I was able to push the button to shut the fan off. So try setting your clock first and see if that helps.

I have the same problem. Is the light still on inside the microwave? Mine is on and the microwave thinks the door is not shut. I took the top off of the microwave and the latch needs to push down on a switch once shut. The latch was reaching the switch, but I think some spring in the door, pushing the latches down, has broken since it reaches the switch when closed but there isn't any downward force to flip the switch.
I am trying to figure out how to repair the latch but if your light is on when you "shut" the door, you may have the same problem.

Most likely there is a part missing from the door latch mechanism that you need. This probably broke off when the handle failed. It would be a tab or wedge shaped piece of plastic that strikes the door switch and pushes the switch closed when the door is completely shut. You will need to find that piece and glue it back on or get a new handle assembly from Samsung.

It is possible you have one or more door switches that are bad and need replacement.

I have a JVM1850 White microwave-over the oven-installed 3 years ago. Last evening the unit would not turn off. The inside light and fan continued to run, however, the microwave was not working.

All the controls and functions seem to operate, but when completed, the unit remained working, as stated above, with the door opened or closed.

On the DMT2420, that's a bad bottom door switch, or possibly that switch's mount.
The service manual is here and the parts list is here.
You can order Dacor parts by part number from the Pros here.

hello mam
i am having the solution for this problem check the lock terminals for loose connection and if its working and check the magnetron which produses the heat inside the microwave.