First off... you screwed up big time. Unless you connect to a TV that has the ability to display those settings, you're in for a long, hard time. Reason I know is that this is one of the 20 stupid things I did to my box before.
You'll have to BLINDLY navigate your way through to the utility and change it back. Guess, use noise as a guide, use splotches on the screen to assist... whatever. It sucks and it took me an hour and a half of screwing around one day to fix.
Another option is to put the original HD nack in and turn off your chip. Doing this might bring up the menu (withh or without the sound) and set the screen settings in there. I haven't tried this, but it seems like a slim possibility.
Last option is a new Xbox. Good luck.
