1) Use a proper thread title; 'Help !!!!' does not cut it. It needs to be descriptive, many people won't even look at your thread with the title you have now. Edit it.
2) Find Hopper8's 'Odin troubleshooting' thread stickied in General, and go through as many of the troubleshooting steps as many times as you need to in order to get a successful flash with Odin. However, be careful you're only flashing I9100G firmware, flashing anything else will brick your phone (like the 3 part firmware linked in Hopper's thread which can be useful in some situations, do not flash this as it's for I9100).
Do not come back to this thread and say 'But I've tried blah blah blah blah'. You are the only person who can fix your phone at this point, nobody here can do this for you. And by referring you to that thread, I've given you the tools with which you can get it done.
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 ?