Windows media Player 11

This should be a question I shouldn't have to ask here. But when i tried tech
help, they said they couldn't help me. I tried the info listed, but they
didn't even have WMP 11 listed! And trying the tech help listed would make me
pay for it. Ridiculous! The problem is simple. I have a media player that
came with the computer. According to the book, it plays audio, videos and
DVDs. Everything works but the DVD player. I tried the Checkup Tool. It says
I have no DVD decoder. I don't want to buy one, so I installed WMP 11. DVDs
still don't play, and it still says I don't have a DVD decoder. Was there one
one in the Media Player? If not, is there one i can get for free? The
company had the info, and I gave them a way to check it , and got no help.
But then if i did, I wouldn't have to pay them! Is there a simple solution to
this, or have i misunderstood everything? Thanks!