Remove the cover and discharge the capacitor (after you have unplugged it, of course). Disconnect the power transformer secondary wires (these are the wires going to the capacitor and the magnetron). Plug the machine back in and select a cooking time and while it's running, check for 120VAC at the transformer primary wires. If no voltage (or considerably lower than 120V), the problem is in the control board. If you get the proper voltage, the problem is one of the high voltage components. Post your results.