My microwave did not work but now it does... what gives?

Maybe it overheated and tripped the high temp thermo button. Later the overheat thermo button reset and all has been restored! (?)

Many have or used to have internal cut outs, that reset themselves. I had one must have been 20 to 25 years ago, new from sears. That would run about two minutes and cut out, a few minutes later it was ready to go again. Turned out that the fan had somehow become jammed inside so it could not cool itself down quick enough. No issues until it finally died about 4 years ago.

Did you have to move the microwave, even a little, to plug in other appliances in the same outlet? If you did, then it's likely there's a break in the wires inside the microwave's cord, and that moving it made the broken ends of the wire touch again.

Perhaps there was a brown-out in your area, and the voltage just didn't get high enough to get the microwave going? And now the brown-out is over.