have you sorted this yet?
if you have a backup on your pc you can use xbhdm to do it.
if the backup is on the xbox drive then you HAVE to use a chip, there is no other way around it.
trust me i know, i did the same to two xboxes (thought i would have learnt wouldnt u?)
i ended up buying a chip to lock it, cost 20 quid from online shop gives u so much more to do with your xbox too.
if you want any help pm me
Regards
Saint