Xbox 360/Undocumented Commands

Reset video
To reset the video settings, boot from the Guide Button on a controller (wired or wireless) and then hold Y + RT.

Clear download cache
To clear the download cache (updates):
 * 1) Go to the system blade and choose memory.
 * 2) Highlight your hard drive and press Y.
 * 3) Then press X, X, LB, RB, X, X. Do not switch the Xbox off!
 * 4) A dialog will appear asking if you wish to perform maintenance. Choose yes.