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?