Well...what you can do is use that EEPROM that you backed up to your PC when you did the softmod (you DID back up your EEPROM to your PC, didn't you?) and a stock C drive image (can be found on a lot of autoinstaller discs such as slayers), and use that to build an XboxHDM disk to rebuild your C drive. Then redo the softmod (preferably with Krayzie's NDURE installer this time).
Now, if you didn't remember to back your EEPROM up to the PC when you did the softmod, you have 3 options.
1) Hotswap the HDD using XboxHDM and get the stock C files on that way without the need for an EEPROM (free, but there are risks involved).
2) Build an EEPROM reader to get your EEPROM then use that to build the XboxHDM disk (cheap, but a pain in the ass).
3) Install a modchip and fix your drive with a bootdisk (as cheap or expensive as you want, but probably the safest option provided you either go with a solderless solution, or know how to solder).