you need to find out what game it was modded with ( mech assult - splinter cell - oo7 AUF )
if your lucky you'll still ahve the game save exploit on your harddrive.
you can reinstall your mod and be back to good in a matter of minutes.
if not......
please say you backed up your eeprom
if you did you are in luck, but require a little more work and time.
check out the xboxhdm tut
http://www.smdepot.net/forum/index.php?topic=85.0use your eeprom and rebuild your xbox harddrive with your PC
I bet you still have the game save on your xbox that was used to mod it, so get in touch with the person that modded it and have him load it up and fix it. or if you want to do it yourself go rent it or buy it. ( OLD VERSIONS ONLY - NOT PLATNIUM )
if you have to use the xboxhdm way with your eeprom, I suggest using a different computer and keeping in touch with our incredible live help room that has done this many times.
http://www.smdepot.net/irc/chat.phpgood luck and let us know what works for you.
BOOST