I've recently updated the OS for my Blackberry 8320 to 4.5.0.69. Since then it can't find the mobile netowork (Wi-Fi and Bluetooth are working fine), and when I put my SIM card into another blackberry it works fine as well. I think there could be something blocking my SIM card but I don't know. Can anyone help?

Well something went wrong while you was installing the new Firmware....close everything and re flash the firmware as in reinstall it on your BB i think you was doing something on ur computer while you was updated it....it MIGHT i dunno but everytiime something went wrong while i installing the new firmware i just do it again and the second time always works out for me.... Give this a try....