I was reheating food from the fridge that had to defrost a little bit. I had reheated about four types of food, the microwave made a sound, and it stopped working. I had taken the food out and touched the top of the microwave. It was hot so I had unplugged it and let it cool down. What do I do now to get it to work again?
Three possible things to consider: steam in the electronics (which should be sealed from that so it would be likely to happen again); sparking when heating the last item, which can confuse the electronics; simple overheating, again of the electronics.
In the latter two cases, leaving it unplugged for a few minutes before trying again should be fine. This is less likely to help if the control circuit has got wet. I assume here that you've got a sensible electrical system with an independent safety earth (ground) and circuit breakers, like I'm familiar with testing appliances on. If you don't, I can't recommend that you test it. I don't suggest that you remove any covers, and definitely don't open it up without it having been unplugged for several hours, or power it up with any covers off, even if you'd do this on other appliances.
The sound made can have been a reversible overtemperature switch (eg a bimetal switch) engaging. If that is the case, the device should work flawlessly again if given enough time to cool down.
If you want to make sure whether the device, IF it works again after cooldown, is safe for continued use, ask the manufacturer support.