Selecting Action When Inserting a DVD or Memory Stick

I've somehow turned off the select box and now when I put in a DVD or insert my MP3 player into the computer they are ignored.  This isn't so much a problem with the MP3 player or a memory stick - I simply go to My Computer and open them from there.  However, no matter what I do I can't get DVDs or CDs to play.  I can burn CDs using the drive and have checked to make sure that all my drivers are up to date.   The coputer does recognise that I've put in the disc and the title of the movie or album appears in the My Computer folder.  It just will not play, even when I try to open it directly from Media Player.  All the seperate files the DVD contain show up, but trying to open any of them results in nothing.

I'm running Windows 7 on a Dell Inspiron N4010 and I'd very much like to figure out how I got rid of the action selection box and how to get it back.

Thanks,

Kureo