You may have a bad keypad, which in many cases can be replaced. If you have a Panasonic or Quasar unit, you can order parts here: http://www.pasc.panasonic.com/epartr or at Tritronics here: http://www.wehaveparts.com A bad keypad may be damaged, worn out due to age, or it may have gotten wet or otherwise contaminated. Moisture and contamination can be caused by spraying of cleaners, by storing the microwave in an unheated garage or shed, or infestation. I warn my customers to never spray cleaner directly onto the microwave keypad, since the liquid can get inside and "lock up" or even ruin the keypad or controller. Apply an alcohol-based cleaner (such as the purple kind) to a cloth (paper towels can scratch) and gently wipe it off. I suggest to my customers that they NEVER use any ammonia-based cleaner (like the blue stuff) on a microwave, since the ammonia will crack and distort polycarbonate plastics.
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