Hello there! I've been happily using a 2010 Mac Pro since March with a Radeon 5870 card and two Apple displays connected to the card with mini-displayport cables. Recently, after I installed Lion, the secondary screen has been acting strangely; sometimes, while I can move my cursor without any problem on it, I can't click on anything. I click and the program, such as Apple Mail or Reason, just doesn't respond in any way. Moving the program window to the main screen solves the problem. Moreover the secondary monitor sometimes shuts down for a second, displacing in the meantime all my windows to the main one. It always comes back instantly. Finally, when I use Windows 7 the secondary screen isn't even recognized anymore; it stays black and windows doesn't see it. I tried of course to unplug and reconnect both monitors a few times but the problem, which in Lion is sporadic, remains. Any ideas?