If microwave does not work

could be:

bad switch = likely = could also be a worn actuator

bad HV diode = likely especially if you smelt anything burning recently

Bad HV capacitor = less likely

Bad control bd = less likely

Bad magnetron = very unlikely

Any of that requires unplugging, removing cover, discharging HV capacitor, visual inspection of diode and capacitor, ohmmeter inspection of switches to confirm they operate, Diode function of DVM to verify diode. If everything checks out, the bd may be bad. There are usually relays on the board that can be replaced, but replacing the bd may be economically not worth it.