What resolution did you change it to, and does the TV support it?
Some Operating Systems have the option of changing back automatically after 15 seconds if the new resolution doesn't work and no keyboard input is given. Is that not the case with Macs?
Purchased a Mac Mini to be able to surf the web using the Samsung 7000 as the monitor. Hooked everything up. It all worked fine when fired up. Got right in to my email with no problem. It was a good display on the screen. After attempting to increase the image size, I got a black screen with a message that this is an incompatible signal. I have been unable to display anything since. Obviously with no display, this computer hookup is dead in the water. Help!?