External display not working in closed lid (closed clamshell)

I have used my Macbook 2.26 with my 23" Samsung 1080p LCD for many months. I recently decided to permanently work with a wireless keyboard and mouse with the lid closed. I use a Monoprice USB + MiniDisplay port adapter.

The first time i did it, i closed the lid and it immediately started working. no worries. I decided to switch my adapter to my large 40" to watch a movie last night. It worked fine and I switched back to 1080i so that it would work on this old tv. Everything fine, went to bed.

Woke up today and switched it back. Nothing. Opened it up and had to reboot because couldnt get a picture to pop up. Now, it only works in open lid non-mirrored function. If I close it, it immediately says "mode not supported" on my TV, even though the adapter lights up indicating that the computer is waking. It seems that there is some disconnect between the computer's output resolution and the monitor. I even tried it on the other TV - same result.

Any ideas what is going on? I have tried adjusting to almost every setting on earth - nothing doing.

Thanks for any help!

First thing I'd try is resetting the PRAM on the computer. Unplug all externals, shut down the computer. Press the power button and then immediately hold down the Command-Option-P-R keys simultaneously, and allow the unit to reboot-chime 3-4 times. Once it's cycled through a few times, release the keys and allow it to boot normally. Try the video again.

Thanks, but didnt work

tried the PRAM reboot. Let it reboot three times and then start up. plugged the connections back in and closed it. Nothing. Same error as before.

Anything else?

Thanks

Is it possible the Monoprice DisplayPort adapter went bad? I've purchased a few of them, and so far so good, but it's certainly possible. Any other adapters to test?