1) I9100 = no NFC. If that phone has NFC capabilities, it's not an I9100. It will more than likely be an I9100P.
2) If the IMEI (in phone settings) has changed to '0049...' (Do not post your actual IMEI here), you might be in a bit of trouble. If the phone is an I9100P, download I9100P firmware from Samfirmware & flash that; hopefully the IMEI will come back. If the IMEI doesn't return, flash another firmware, and another and so on.
If it is an I9100 & you're merely confused about the NFC thing, download a bunch of I9100 firmwares & flash.
If after flashing a bunch of firmwares you still have the generic IMEI, try one/more of the many 'guides' on here which claim to be able to recover your IMEI without an EFS backup (no idea if any of them work or not).
If you still can't get your IMEI back, take it to a local mobile repair shop; many have equipment which can write the IMEI back to the device fairly cheaply.
Edit - Use a descriptive thread title in future - 'Help me please' is more than likely the reason you've been sitting for 18 hrs waiting for help, many people won't even look at your thread without a title which gives some idea of whatever problem you're facing/question you have.
If it's important enough to cause you grief if it's lost, back it up. No excuses
Trolling for thanks is lame
Does Samsung's auto-brightness implementation crap drive you to self-harm ? A solution !
Failure to search is the leading cause of male impotence on XDA
If you don't know how to recover if things go wrong, what are you doing flashing custom roms ?