Changed region on computer dvd player now it won't work?

I recently changed the region of my computer's dvd player to region 2 instead of the original reason 1, and it worked fine playing my region 2 dvds...but now that I've changed it back to region 1, no dvds will play! When I put them in they start in media player, but there's no sound and the picture is sped up. What happened to my computer, can I fix it...?