Have you tried booting into recovery and wiping everything before flashing system? Also you're sure you have the right system.img? Maybe re-download the files from google and try again?
---------- Post added at 09:23 AM ---------- Previous post was at 09:22 AM ----------
also, do you have any nandroids or downloaded ROMs on the phone? If so, you could try flashing CWM, and then booting into it and restoring the nandroid or installing a ROM.