Softmod woes

Hi

A while ago I did a softmod on my friend's xbox using the softmod installer deluxe disc and splinter cell exploit. I made some stupid mistakes, namely that the dash wasn't updated to the most current version and also that I may have installed the dash over the standard one. Anyway, when I turned it on I was greeted with the GSOD error message and that, i'm afraid, was that. I'm sure that this is now f***** because the xbox isn't chipped but is there any possibility of a recovery. I made sure to backup the original installation and eeprom on the drive (not sure if that helps). I've had to give him my softmodded xbox for the while and it would be nice to get it back. I've also got a chipped xbox myself so I'm not sure if I could do anything with this to sort out the GSOD one. Any help most appreciated!