I have an old Samsung Galaxy Note II. Rooted.
One day it went off. When I restarted it, it went to a somehow hybrid state between factory and the status it had before crashing, i.e. I had to reinstall everything, everything on mobile sd was gone, BUT it retained root.
Now everything eksr is working (besides some problems due to the old battery, it freeze or shut off every time battery level is about 80%) except for the fact that it does NOT recognise Sim cards (which are ok when mounted to different devices). Messages are "not registered on network" and "insert a SIM card".
I am still using the phone for everything it does not directly require a network registration (photography, reading, games, surfing on WiFi ecc).
Is there a way to correct whatever got corrupted? A number? In fact the phone does receive some signal from the provider (3 to 4 bars) selected - which is that of the unrecognised Sim.
With a new battery it could be a nice device. I love note 2.