I bought a used Nexus S that is on version 2.3.6.
It does not seem to be reading any SIM cards and the baseband version is listed as unknown. I think it may be on a custom ROM because of this. I want to flash it back to a stock ROM but have no idea where to start. My Nexus S is I9020A so I downloaded 4.1.1 from here but have no idea where to go from here.
Are there any easy to follow guides? And am I even on the right track here?