Help with DVI to Video

hi, I regularly use my dvi to video adapter to watch movies from my mac on my tv. i have never had any problems until this morning. I was trying to watch a movie, but I wasn't happy with the display size/resolution so i went into system preferences to try a different display. when i tried switching, the TV screen went to black and white and started flashing, and is now unwatchable. The image on the computer itself looks fine though... any suggestions of what is going on? I now it isn't the tv because I tried my old ibook and it is showing up on the tv just fine.

any help would really be appreciated