I've found from repairing and "hacking" microwaves that they all follow a flow chart when a symptom prevents it from working normally.
From what I can recall about the symptom "unit not heating" and if that is the only symptom, the primary parts that are suspect are (in order of most likely the problem): 1). the High Voltage Diode (HVD). It should show continuity in one direction only. These are subject to large jolts of energy and if they are low quality will fail. Not very expensive to purchase and quickly replaced. 2). the Magnetron has parts that if jolted or jarred will break easily. It is difficult to test with anything but special tools made for the magnetron. Check for the correct voltage at its' terminals and if all other components are working replace it. 3).the Capacitor will go south eventually no matter what quality. Visually check for bulging in the wall and replace if found. After discharging, check with a DVM by setting the dial to ohms. When the probes touch each terminal the reading should be rising. Alternate the probes and the reading should go down. Replace if it shows continuous continuity.
With todays low priced microwaves, unless you are repairing them to learn or as recreation (or your being paid), replace the non-working unit with a new one.
On a side note, I've learned a lot about repairing microwaves with this book by Homer L. Davidson, "Troubleshooting and Repairing Microwaves".