But if you want any detailed repair advice, you must post the model
number and manufacturer, and you should be able to perform some basic
troubleshooting first.
For microwave ovens, this means first understanding the very important
safety rules for working on them available at:
http://www.repairfaq.org/sam/micfaq.htm#micsaf
Then, you need to be able to do some tests such as checking if the
keyboard accepts commands, the door switches operate correctly, and
while following the safety rules, you should be able to check whether
certain voltages are available at the correct areas and component
locations. You need to know how to test components like diodes,
switches, capacitors, and fuses.
For safety reasons, if you do not know how to do these things, you
should take your microwave to a qualified technician for an estimate on
the repair. Otherwise you could do a lot more damage to it, or even
worse you can be killed or injured by the high voltage, high current
circuits inside. (Microwave ovens are the most dangerous home appliance
to work on if you're not careful.)
Don't take any of this the wrong way. Members of this group ENCOURAGE
you to do your own repairs, but safety is a priority.