Problem playing DVD's on my laptop?

When I put in a DVD it says WMP cannot play this DVD video. You might need to change your display setting by lowing the color and screen resolution. I shouldn't have to do this because it has worked fine before. Anyway, I tried that and nothing. I tried uninstalling the CD/DVD drive and nothing. I reinstalled WMP and nothing. I can't play any DVD's or even any videos that are already on my computer. Could it be something with the video card or codecs? I'm not sure what else to do. Any answers would be greatly apprciated.