Maytag over the range microwave oven - which component runs all power?

1. A fuse or circuit breaker in your home electrical panel.

2. A fuse inside the unit.

3. The power transformer inside the unit.

If (1), obviously you can correct the problem quickly yourself, but if it trips or blows again right away, there must be something wrong with the circuit or unit, and an electrician or appliance repair/replacement will be needed.

If (2), and you were handy enough to fix such things, I imagine you would have found and replaced it before posting. Since you wrote here, I must assume that you don't know how to safely work on appliances that can produce deadly high voltages inside, so again I would recommend having the unit professionally repaired, or replacing it. If you found and replaced the fuse, and it blew again immediately, the most likely culprit is (3):

If (3), usually the cost to obtain and replace the transformer is not economically sound versus replacing the whole unit, unless you happen to find a working identical model at a bargain price in a thrift shop, salvage center, etc. and are capable of swapping the parts yourself.