First call your life insurance agent and make sure your policy is up to date. Wear non-grounding shoes. These things are very dangerous.
Unplug your microwave. Although it might seem like no electrical current could possibly be running through your appliance, it could still have stored electrical current somewhere in the system. Be safe rather than sorry and unplug it before you begin.
Find the wiring diagram for your model of GE microwave. You can contact GE directly to get this if you cannot locate your owner's manual. Note the fuse locations and get a screwdriver. Some GE fuses are located under the louvers, while others are located in the door.
Open up the microwave and locate the blown fuse. Sometimes you cannot determine a blown fuse by visual inspection so check it with a multimeter for continuity across the terminals.
Replace the blown fuse. Go to your local hardware store and pick up a matching fuse. Make sure you check the model numbers of the fuse as well to be sure you get the right component. Install the new fuse and put everything back together.
Check the continuity of the circuit if you continue to have power problems. If you have a problem with continuity in the circuit, then you may have a bigger problem than just a blown fuse. Sometimes a power surge will fry a GE microwave's circuit board, which you will need to replace.
john vrtiak, usually we like to refer questions about microwaves on here. Those things pack a lot of oomph and are not a good DIY'er (unless experienced) project. Anyhow, the fuse change seems to be straight forward enough, it is behind the control panel.
Remove 2 screws from front vent cover and removed vent cover
Remove one screw from top of display
Gently push display panel up about 1/4 inch and tilt the top toward the front.
Disconnect 3 thin gauge Molex connectors
Disconnect 1 heavy gauge connector
Remove screw from grounding wire at bottom of display circuit board
Remove display panel completely
Remove grill from above display area
To the left is a 2 x2 inch square board
Coil, capacitor and fuse block
Match fuse rating and replace
Number 47 on the diagram is the fuse. Hope this helps, good luck.