Disconnect power. Disconnect the leads to the element. Put your meter on ohms, and measure resistance accross the Element. If you have a very high reading or infinity the element is bad. If you have a low ohm reading, the element is probably ok. Next check the Thermostat. It should also have a very low ohm reading when the pot is cold. This is the part most likely to fail. Lyman pots have a habit of short life on temperture controls. I experienced the same problems, and bought an RCBS, that I've had for about eight years, and cast thousands of bullets.
If the thermostat or element s bad you might go to the Lyman Webb sight and see about getting a replacement part.
Good luck
Jim