My N900 won't register the sim card. I flashed my n900 to PR 1.3 after it got stuck in a reboot loop. Now everything except the phone function works. I tried searching but I did not find anything that helped. Is it a hardware issue or is there any way to solve it? any help would be appreciated.
Thanks.

Is the SIM holder clicked into place properly?

I had a lot of trouble with the SIM not being recognised until I realised that the SIM holder actually locks into place.