I have a Mac Pro (late 2007) running OSX 10.7.5. I want to remove the monitor and use it headless via Mac's built-in screen sharing (from a brand new iMac). When I screen shared and the monitor was still attached to the Mac Pro, it worked great. But when I disconnected the monitor and screen shared again, the resolution was 800 x 600. I tried changing the resolution, but it won't change to anything other than 800 x 600.