Since upgrading to Yosemite, my 2010 MBP is unable to play video files of any kind on any app other than QuickTime. I prefer VLC player to QuickTime for a number of reasons, but it just freezes/spinning wheel when I attempt to load a video file. Same goes for mplayerx and a number of other apps I tried to download both on and off the sandbox. In other news, when I try to log off to switch users, mac goes to a black screen, no cursor etc. Also, sometimes when trying to revive the mac from sleep, it will go to an illuminated gray screen, but then quickly back to a black screen. This happens when I press esc or the power button. I have reset pram, smc (I think), used an app to free up as much ram as possible, still these problems persist. I have repaired disk permissions as well. Any help would be greatly appreciated.