If you have a XBox 260 that you move from place to place, you may run into the issue where you connect it to a new TV or monitor and you can't see anything because the video settings are different than what your XBox 360 is configured for. When this happens, you can't even get to the screen that allows you to set the video settings, so you are basically screwed. If this happens to you, there is a fix.

Remove the disc from your XBox 360, turn it off and then turn it back on. While your XBox is restarting, hold down the Y button on the controller and pull the right trigger.

This will reset the video settings on your XBox 360 and then your console will restart. Once the restart is complete you should be able to see the screen again without any problems.