Thank you for your question and I understand your concern.
You could be describing a touch pad or control board issue. I have a GE table top microwave and there are times that I have to push START twice before it would start and I haven't been able to diagnose which one is at fault because there is no test procedure for the touch pad. Some models will have a key pad test so a service technician could test to see if the Start pad is working.
I am sorry, but we do not give repair information on microwave ovens because they are inherently dangerous to service. Microwaves contain high voltage internal components that can retain a lethal electrical charge even when the microwave is completely unplugged. Door repairs and adjustments, even minor ones, can cause microwave leakage, and a microwave shielding leakage test must be performed using a survey meter after any microwave service. That's why I strongly warn you to have this repair handled only by a qualified service technician. You can schedule service online with Sears Home Services or by calling 1-800-4-MY-HOME.
Normally at ManageMyLife.com we like to help you with all of your repairs, but our expert advice is that microwaves are just too dangerous.