I have a late 2011 MBP hooked to a Thunderbolt display. This afternoon I started getting white screen. It will be working fine and then I get white screen all of a sudden. I have to hold down the power button to shut it off and then restart it. It will work fine for about 30 minutes and then do it again. It has down it about 3 times in a down now, starting 1.5 hours ago. Any ideas? Could it be something with the ATD causing this? Thanks for any help.