How can I disable the Macbook keyboard (from startup) How can I disable the Macbook builtin keyboard which is defective (looks like the Shift key is always pressed). I need this in order to avoid starting with the Shift key pressed otherwise the Macbook always starts in Safe Boot mode.

I have an external keyboard attached now with which I can work in Safe Boot mode.
You can try this to disable the keyboard kext, although I'm not sure if it will work at boot time. Enter this command in Terminal:

sudo kextunload /System/Library/Extensions/AppleUSBTopCase.kext/Contents/PlugIns/AppleUSBTCKeyboard.kext/


To re-enable the keyboard kext, type

sudo kextload /System/Library/Extensions/AppleUSBTopCase.kext/Contents/PlugIns/AppleUSBTCKeyboard.kext/


Source: http://forums.macrumors.com/showthread.php?t=433407

To bypass Safe Boot with a stuck Shift key, hold down alt at startup and select the Mac OS X bootable partition.