It is difficult to give an exact answer from your question since more information is needed. To narrow the fault down a technician will make a number of observations and tests. You have made a start but here are a few more:
# Is the display indicating anything? Since you outlet is working it is therefore a fault in the microwave.
# Unplug the microwave and remove the covers. There is usually no safely issues in working on an unplugged microwave except that on very rare occasions the high voltage capacitor may remain charged. Shorting it is a quick indication whether is charged and will also make it safe.
# Check the main fuse (usually located on a circuit board where the power cable terminates.
# If it is blown there would be any number of causes including a power surge, faulty door switches, etc. A technician will be able to determine the cause.