I assume you are running the DVD audio and video through the AV 7000, and you have already indicated that you have made a component connection to the monitor (the plural "terminals" implies audio as well, which suggests you have the add-on speakers). You don't indicate the Xbox connection method, so I have to assume that's through the AV 7000 as well.

One thing I found on the monitor is the S-Video input takes precedence over component video, so only the former will work if both are used (BTW, there's a noticeable improvement in picture quality using S-Video, particularly with the DVD player). Also, mixing the two types on the receiver may be to blame.