MacBook Pro 15" 2010 keyboard won't work in login screen - Yosemite I did an update to Yosemite yesterday, but today I turned the computer on and tried to type my password in. I couldn't because the keys I P A D K L M C don't seem to be working, I have tried three different keyboards and none work. Two of the keyboards are official Apple. I tried them in my windows laptop and all the keys are working fine. I then booted into the recovery on the MBP and I could type with all the keys. I thought it was fixed so restarted. I then had the exact same problem and am at a loss of what to do. I've tried Apple support, but they are about as useful as a chocolate tea pot. Any help would be much appreciated. Thanks.
Try this...

Start your Mac from the recovery partition. Once it's booted, go to the Utilities menu item and select Terminal. Type in the following command (substituting the OS X startup disk name if different from Macintosh HD)...

rm /Volumes/"Macintosh HD"/Library/Preferences/com.apple.HIToolbox.plist


...and then restart your MacBook.