Normally this would be a bad door switch, but it may also be a broken tab on the door switch mounts.
On that model, the fuse is located on the door switch mounts (called the door hook) so you've been there, and that's the area to focus on.
The hooklike projecitons on the door (called the latch heads) are held secure by the door hook so the switches are activated properly.
Sometimes a little tab breaks on the door hook which causes the switch to rotate out of place.
Other times, one or more switch will stick or short, and blow the fuse or breaker.
If you or a friend decide to look into it, we have critical safety information, info on door switch diagnosis and replacement, and disassembly information at our site, and our link is at our listing here on FixYa: http://tinyurl.com/yzjozk
You can order Sharp parts from Tritronics at http://www.wehaveparts.com
You can find exploded view diagrams for this model here: http://www3.sears.com/
(3 is correct)
Here is some extra info for you:
A microwave can be dead for many reasons.
If it goes dead for a while during or after cooking then comes back on, the magnetron is probably overheating and causing the magnetron thermostat to open. Then when it cools, it closes the circuit and allows power through again.
If it's intermittent or random, it may be a bad connection, usually on the control board or a loose fuse holder.
If it went dead almost immediately after pressing the Start pad, that's usually a shorted high-voltage capacitor.
If it went dead a few seconds after pressing the Start pad, that's usually a failing high-voltage transformer.
If it goes dead or blows the breaker when you plug it in or open or close the door, then there's a problem with a door switch or door switch mount.
If the fuse is good, it may be an open thermostat or thermal cutout on or near the magnetron or on top of the cavity / body of the oven.
We're happy to help and we appreciate your thoughtful rating of our answer.