Part of the keypad doesn't work, how can it be

the only way to fix it is have a new kye pad fitted for you, its a comon fult if the kyes are prest to hard or had a lot of use, on the back of each button is a carbon pad witch presses on a copper strip, its got dirt or grees behind it or its just plan warn out,, best bet is buy a new microwave, to fix yours would cost a boom,
and be warned,,, if you are thinking of going inside of this unit, if you tuch it in the wrong place its very likely to kill you!!!!!!!!
there will be 1000;s of volts kicking about inside it,, volts kill,,,,,
1000's of volts kill quickly,,,,, be safe buy a new one