GE Microwave jvm1651BB will not heat

Question

I have a GE Spacemaker Microwave oven model jvm1651BB 003 and it comes on but will not heat. I called a repair place to come look at it and he told me over the phone they will replace 3 parts. Do you know what is wrong with the Microwave and does it only need 3 parts replaced and is it hard to do? Could I do it myself?