I have a MacBookPro "15; late 2011, and have problems with the final release of Yosemite 10.10.3. Also to allready be clear, my motherboard has been replaced under the Apple Repair Program. I have the following problems i can't get resolved: 1. Sometimes starting up is stuck on just a grey screen (no Apple logo) 2. Sometimes logging in just gives a black screen with a moveabble mouse pointer, Option+Control+Esc gives a window, but no running tasks to stop. 3. Screensaver not kicking in 4. Going from Sleep mode (opening the lid), just gives the black screen with pointer (see 2nd issue) 5. Restarting or closing down (chosen in Apple menu) , gives just again the black screen etc. Anybody has a possible solution?