I'm really not sure, but flashing the wrong ROM could have messed up some partitions. Have you tried formatting /system as well?
I think the best thing you should do is to run a RUU. You don't have to be s-off, but then you need the right one for you. Since you don't have a stable system right now, I don't see a way how you could achieve s-off right now. Could you please post the output of this command: fastboot getvar all