Responder a:MacBook Pro 15" Early 2011 Stuck on white screenThere is only one solution to me that is helpful indeed. Shut down computer manually. Wait 10 seconds. Start again and when you hear the first sound/signal, press cmd/alt/P/R all at the same time until you hear the second start sound. Then release the keys. At the beginning it worked every time. Later (now) i have to do it up to 4 times. But: it works. Good luck folks!