Media Center wont play my DVDS

The other day, MEDIA CENTER stopped playing DVDs. It is displaying this message... "The DVD may be in use by another application. If all other applications are closed, the display resolution may need to be lowered or the display connection type may not support playback of the DVD." I tried both things that it suggested. and nothing happened. I have a feeling it has something to do with ActiveX and Javascript because when I tried using my NETFLIX Watch Instantly, it told me that ActiveX and Javascript were enable or blocked or something...I don't remember. I don't know what to do!