My Mac Book Pro won't boot
I had just installed Mainstage from the App store and had loaded the app.
Nothing else was running at all and I left my Mac downloading a new sound set. When I came back, 20 mins later, my computer had turned itself off and now won't turn back on again - not even in safe mode. It comes up with the Apple logo and then turns itself off immediately.
Someone please help ...
MacBook Pro, OS X Mountain Lion (10.8.1)