Did you reset or do any kind of firmware update on the TV since the MacBook was able to connect? You might edit the name of the input to DVI or DVI-PC as outlined on Pg. 12 of the manual.
MENU > INPUT > EDIT NAME > DVI or DVI PC > [Enter]
You'll also want to make sure that your computer is sending a resolution that is supported by the TV. (1920x1080 @ 60Hz) Also, if applicable, check to make sure that your overscan settings in the video card are set to 0.
Does that help?
I bought my Samsung 55" LED tv a couple of months ago. I also bought a Dynex Mini DisplayPort DVI Adaptor with it. I successfully connected the TV to my MacBookPro and could watch movies off my laptop on the LED screen. But it suddenly stopped working yesterday..I saw some white noise and rapid flickering on the tv screen, and now it says 'No signal' on a blank screen.
I verified that I can see picture when I connect the cable to a Dell PC, but for some reason, it doesn't work on my Mac. The Mac sometimes detects the Samsung screen (via Displays > Detect Displays) and sometimes doesn't. I saw another post where a Samsung tech person said to increase Picture Mode to 'Screen Fit', but this option is grayed out on my tv, hence unselectable.
Any ideas? Please help!! I hope its not a problem with the Mac.