Why is my disc player won't open?

There may a game disk or DVD lodged in the player. My suggestion is to first investigate and attempt all manual options to open or fix the player prior to replacing it. If all options fail, then replacement may be your only option. Here is some helpful information:

There is an emergency eject button that can be found directly under the Xbox 360 logo, but the faceplate must first be removed. See Microsoft's Directions to Manually Eject the Disk Tray.

For another useful link, see iFixit's How to Remove a Stuck Game from an Xbox 360. Either of these links should be most helpful.

If that does not work, this iFixit link to repair the Optical Drive should work. See Repairing Xbox 360 Stuck Optical Drive.

Lastly, when all solutions above have failed, you may most likely need to replace the Optical Drive. It is a bit difficult, but not impossible to do. See iFixit's Xbox 360 Optical Drive Replacement.