There are known problems with Lion/Mountain Lion and projectors. Have a look at this thread for some suggestions: https://discussions.apple.com/thread/4159965?start=0&tstart=0 . The most important point seems to be that the projector must be on before you start the Mac. And don't just start from sleep; do a proper reboot.
There are known problems with Lion/Mountain Lion and projectors. Have a look at this thread for some suggestions: https://discussions.apple.com/thread/4159965?start=0&tstart=0 . The most important point seems to be that the projector must be on before you start the Mac. And don't just start from sleep; do a proper reboot.