Mac boot menu not showing up with different keyboards I have a Macbook White from 2010. I have been using it for a while and everything works except the internal keyboard which is broken because of a tea spill. An external PC-keyboard (USB) is attached though but it doesn't work properly.

I had installed Yosemite and it worked fine, but later I decided to reinstall Mountain Lion again.

I tried to enter the boot menu with the alt-button to reboot to my second partition but it didn't work. 

So I've changed the Start Volume in the System Preferences in Yosemite which was successful but now I'm stuck in the 'Mountain Lion Install'-partition which just loads to a grey screen and nothing else happens.

Is there any solution guys?
I also use a non-mac keyboard and have seen the issue where it skips the boot menu. The native keyboard works both from a cold boot and a soft reboot. The 3rd party keyboard only works from a cold boot and not from a reboot. You should be able to power down your Mac and power it back on and have the boot menu work with any keyboard.

I've also read a few places that it matters which USB port you use for the third party keyboard (for the boot menu specifically). You could try moving the keyboard around to see if you get the desired behavior. YMMV.