The F7 indicates that power was lost to the magnetron. You could have either a failed main control board or a failed inverter board. This type of internal component failure will need to be diagnosed and repaired by a technician. Microwaves are inherently dangerous to service. Internal capacitors can retain a lethal electrical charge even when the microwave is completely unplugged. A microwave radiation leakage test must be performed on the unit following any internal repair. These are the reasons that I recommend that you have a technician fix this microwave problem.
Most control boards are not returnable once they are purchased. Without diagnosing the failure, there is not way to know exactly which component has failed.