Whirlpool over the range microwave model MH7140XFQ?

Sept 1998 model MH7140XFQ the keypad is frozen up cannot work any numbers or e-z choice menu except the numbers 6 and 1 and start button the light will not go off froze up last night after making pasta on the range condensation has done this before and then it worked after opening and closing unit now will not work at all except for that 61 seconds that I can use. Heats up fine. Help frustrated!!