The food never even warms.

If the microwave still light up, then it's not a fuse. the ceramic fuses are on the incoming power supply, so if it blows, you'll have nothing, as in no lights, fan, turntable, etc. There are numerous bi-metal fuses scattered around the unit, designed and located to detect overheat situations, but they should reset after cool down. Possible problem could be the magnetron itself (the thing that generates the microwaves), the super capacitor, or any of a miriad of electronic components on the circuit boards. As oldturkey03 mentioned, the fuse is easily replaced. Worst part is getting to most of them, which requires taking the unit down and removing a dozen or so screws that hold the outer shell on (and then remembering which screws go where upon reassembly). Anything else should be done by a professional. Unfortunately, given what it costs to have a repair done as opposed to simply replacing the unit, the latter is the easier and likely less costly route to take.