I'm wondering if there is some sort of corrupt RAM causing the issue? I've tried to do a Factory Reset, but this also fails and I end up back at square one. So I tried Nexus Root Tookit to go back to stock (all I've done previously is unlock the bootloader, no root). This also fails:
sending 'bootloader' (3911 KB)...
OKAY [ 0.516s]
FAILED (remote: (InvalidState))
finished. total time: 0.745s
Any suggestions on what to try next?
This may of course be a hardware fault, the device was bought in Summer 2012 on release.