I have an older MacBook (model 2,1). I run dual monitors all the time - the laptop screen and a flatscreen. No problems - works fine. I do a ton of presentations for clients - using their projectors - and until two weeks ago have had ZERO problems. BUT something has happened -- no matter what model of projector is used, it has become impossible to use the projector as the 2nd monitor. The monitor display preferences recognizes the projector as a 2nd monitor, but the projectors don't recognize the signal - "no signal." It has worked perfectly fine for years and now it doesn't. I use Lion 10.7.4 It's just strange that the monitor on my desk works fine, and projectors USED to work fine, but no longer. Any ideas ?? Is there a way to check my video card?