You have to check for continuity the fuse which is located in the line filter and the cavity thermostat (#1121 at the
diagram) which is located on the top right side of the microwave.
GE does not sell the fuse separate. It comes as a part of the line filter, but you probably can buy it at any hardware store. If this fuse is blown, you have to check the door switches.
- The line filter
Part number: WB27X10741 
- The universal micro switch, substitutes interlock switch as well as monitor switch
Part number: WB24X10103 
- The cavity thermostat
Part number: WB27X10909 
Here are the breakdown diagrams and
Replacement parts for General Electric ZE2160SF04 MICROWAVE | AppliancePartsPros.com
Gene.