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.