Remove your battery and your sum card.
Wait 10 seconds put them back in and reboot.
If problem still exists go to
settings > wireless and networks > mobile networks. Select your carrier network.
Sent from my GT-I9100 using XDA
Stop being lazy & try a bunch of ICS roms till you find one you like :-| No excuse for not doing so given how simple/quick it is to flash a rom in CWM & also to backup/restore.
If like me you download through your carrier network it can take a wh...
I recommend Koud AOSP 4
I'm on this from now and my internet is faster than its ever been.
For some reason this from doesn't come with a file manager I recommend astro or ES. I got astro.
Haven't had it long enough to comment on battery life.