i have same issue. flashed to a rom after cache and date wipe, everything said it completed, then stuck in bootloop and cannot get into recovery or download mode. phone just resets, vibrates and shows s3 logo and then reboots again and again.
switched odin on, but it doesnt even see the phone.+
edit: eventually got download mode working somehow after hours of trying, not sure if it was pulling out battery longer than usual or else. flashed to dmodv6, works absolutely fantastic. STAY AWAY FROM CYANOGEN ROMS