A friend decided to disinfect the keyboard of another friend’s MacBook Air. Some of the keys in her password no longer work, specifically M and P.

The weird thing is, we tried a USB keyboard and those keys also don’t work with the external keyboard - typing M and P get no input.

We also tried the Dvorak layout. The “broken” physical keys work, but the keys that are mapped to M and P then don’t work.

When I log in as a Guest User, the USB keyboard works completely, but that doesn’t help much.

It seems like some kind of software keyboard module got fried? I can’t think of a good explanation.

Currently we can not log in to the computer at all.

Can anyone help us, or at least give some guidance on how we can back up the computer?

  • Please update your question with the specific MacBook model so I can post an image of what cable to disconnect
    – Allan
    Mar 30, 2020 at 7:12

1 Answer 1


Physical damage simply cannot “fry” software; it’s impossible. The most likely cause is that something is shorted in the MacBook keyboard and it’s conflicting with the same signals being sent by the USB keyboard.

Disconnect the keyboard from the logic board and then use use the USB keyboard to login. While it will get you up and running, it’s not a permanent fix. The top case will have to be replaced.

See Keyboard key stuck or not being recognized; how to fix for more details

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