Any errors come up?
If you try and restore, it's just going to restore the Demo. I would
TRY and flash the latest update after a complete wipe and see if that gets you anywhere:
http://www.amazon.com/gp/help/custom...deId=200790620
If not, then you have to flash 4.2 Jelly Bean.
To mount the drive in TWRP, click the Mount button.
I don't know if anything else is needed, I haven't done this for months now.