When you and your friend were doing this, did you happen to backup your eeprom? That is the first thing you should do, because if you back it up, no matter what happens, it is fixable. Most likely, the HDD is unlocked. When you try and boot it, do you get an error code? (Top left corner) If so, what is it? 5? 21? Another possibility is he installed the fonts to a new dashboard that is un exploitable. If your xbox is new, it could have the newer kernel which doesn't allow downgrading your dash (rendering the exploits unusable.) Catch me online through one of the contact options (below this post) and I will gladly help. Most important to know is the error code and if you backed up your eeprom. How did you try and apply the exploit? Hotswap or gamesave hack? (Did he actually remove the hdd with the xbox on, or did he use a memory card?) Good luck.