From what I understand. Resetting your Xbox to factory defaults could possibly erase everything on your Xbox. You can however recover your gamertags and download all of your DLC's back for free assuming it's on the account you purchased them with.
Another alternative that I highly recommend that had slipped my mind before is this. When you set the pass code you should have seen the option to put a pass code reset question. If you can answer this question then there will be no need to restore your Xbox.
What if I forgot the answer to my pass code reset question?
Don't fear as you can fix this as well.
You can call customer support to get the console-specific reset code that clears the Flash settings. Clearing the pass code doesn't erase profiles, saved games, downloaded content, or any other vital info. This is looks more preferable than a restore.
If you prefer not to contact Live support through the phones this is also available. You can contact the xbox support tweet fleet who are an awesome set of gamers who work for microsoft but are dedicated to assisting ASAP and also aware of the issues as first and foremost they game.
This should do it, If you have any questions make another reply to this thread or feel free to PM me! Zach