how to fix a sharp carousel microwave after it has been used to heat a lot of food?
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.