I remember reading somewhere here that if you have flashed a diff FW now and then a possibility the last recent kernel is still in the system folder etc....this is maybe the cause of the bootloop.
Since you had confirmed going to download mode is possible..this may work logically...
Why not do the following :
Get your phone rooted via Recovery (there is a thread here by The-E)..Once done flash arco68's CWM Recovery....Boot to recovery n do this :
Factory Format....Wipe n Clear including Delvik...Then go to Mount n Storage wipe every single folder...System...Data...Etc (this will wipe every single data left behind but I assure you the CWM will not be wiped) once done reboot n put the device into DL mode and use Odin to flash back to the stock FW.
From this moment the recovery will be replaced by stock version and the stock FW will be restored....once it boot up..Walla as I had done this over two times :
Best of Luck !!
Sent from my GT-I8150 using xda premium