Something Wrong With My Xbox?

My Xbox 360 (bought it a few yeas ago), will not read games as games. It plays DVDs and I don't know about CDs (haven't tried it). It Connects to the WiFi. But when I put an Xbox 360 game in the console it says 'Play DVD'. I press play and all that comes up is either an Xbox 360 screen, and I have to press the home button and go back to dash board. Or It says, "To play this game, You must put it in an Xbox 360 console." In every language. So I take the disc out and clean it and restart the Xbox, then try it again, same thing happened. Half an hour later the Xbox reads it as a game and I press play. The screen goes black for a few seconds and then a screen pops up and says 'This disc is unreadable' (etc). So I take it out and clean it and it either does the Xbox 360 screen thing or it says the disc is unreadable. What is wrong with my Xbox and how do I fix it? (and if I need to go somewhere to fix it, Where and How Much will it cost?).

Thank you so much for your help ^-^