My 20 Cinema display won't show up after years of pairing perfectly. How do I get it to show up?

I just plugged my cinema display into my MBP13 and I cannot see it. I disconnect and reconnent the display when I travel, and it has worked for years.

In system preferences underr display it does not show up. I tried booting from a differenct drive and it shows up just fine. Unfortunately I don't want to work from a remote USB drive. I've run disk utility just in case there was a permissions issue. I've disconnected and reconnected the DVI adapter as well as display port connection. I've also simply restarted a couple of times. Any ideas about how to get this to work? I know the display is fine because I can see it when I boot from an alternate drive. I don't get it. Please help!!!