See if you can dig up a 3 part stock firmware to flash (assuming you haven't already, a little vague about exactly what you have flashed, I also presume you're talking about an I9100 ?). Could well be a case of corrupted NAND, this is sometimes the case where you seem to get a successful flash but bootloop won't go away & you're still stuck with only download mode. Fix for that is a motherboard replacement, but I wouldn't be calling it just yet.
If you can't find a 3 part firmware (or if you've already tried one), just get hold of as many stock roms (from Samfirmware/AndroidFirmwares.net/Samsung-Updates.com) as you can & flash away; sometimes these cases are fixed by perseverance (the first 10 flashes don't work, but for whatever strange reason the 11th works, for example).
Search for Hopper8's 'Odin troubleshooting' thread & try all the stuff in that thread, might be something really small/obvious that's causing problems here.
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 ?