HELP! Did DVI cable make my tv go letterbox??

I brought a DVI cable over to my nephew who wanted to watch dvd's through his laptop on the 50" Samsung DLP. I tried the cable through the MOTOROLA hdtv cbl box --I got a mssg saying it aint gonna work. Anyway, we proceeded to unplug the dvi from the cbl box and into the laptop-- and we watched some movies-lotsa fun. Today I get a call from my bro-in-law and he says the HD progrmmng is all in letterbox. It is not filling the screen like normal. The sd programs havent been affected. IT IS POSSIBLE AN UNCONNECTED DVI CABLE IS STILL PLUGGED IN!!! My nephew may have just unpluggd his laptop and went on his way. Any ideas how to get the HD (over component in puts) back to normal??