I am running Yosemite 10.10.4 beta on MacBook Pro (15-inch, Early 2011), 2.2 GHz Intel Core i7, 16 GB RAM and 480 GB INTEL SSD, which replaced the 750 GB HDD. It also has a dedicated AMD Radeon 6750 GPU with 1024 DDR RAM. After having the typical GPU issue I replaced the GPU and had peace for a couple of months but the GPU issue returned. Anyway this is not the problem I am writing about. What I am asking help for is the strange behavior that my MBPro sometimes doesn't wake up after being in sleep mode. When opening the MBPro the screen stays dark, the keyboard light doesn't come on. But when I close the MBPro the light on the front right turn on and stays on and the fan starts to run after some time. The only thing I can do is to do a hard reset via power button. But then, when the boot screen with the progress bar and apple logo come up, the bar fills up to one fifth and then the bar and the apple logo disappear. The screen turn greyish blue and nothing else happens. All I can do now is sometimes reboot again via hard reset and then run a diagnostic test by pressing option + d. The test finds no issues (neither the short nor the long version do) and after the test I can reboot without issues. Sometimes it also works when I press option when rebooting and then select the boot drive (SSD). Does anyone know this behavior and where it comes from? Could it come from the faulty GPU. If yes I thought that the computer boots with the integrated GPU and then switches to the deticated GPU after boot up? I also don't think it comes from the beta 10.10.4. Anyway, I appreciate any serious suggestions and hints.