Playing a dvd?

Every time I put in a DVD into my DVD drive to try and screencap, it wont play. It tries to automatically open it in Interactual Player, even when I've uninstalled it from my computer. I would download Power DVD or WinDVD or Virtualdub, whichever one works best, but my dad won't let me download anything. So, I'm trying to make the DVD play in Windows Media Player, but it just....won't, and I have no clue what to do.