this is little thought:
case 1: if you don't have any important data
1. flash recovery like phliz or TWRP , make full Nandroid backup.
2. wipe system, data and cache/dalvik, flash any ROM out of there in Dev section, or stock if you want.
3. done , enjoy your phone again.
case 2: if you do have important data
way 1: 1,2,3 are same as above
4-1: use TB to extract important apps/data from Nandroid backup (I'm not sure if you can fully recover all your datas, but i think it should...)
way 2: or, check out in "about phone" and find your current firmware , and then download from sammobile the same firmware you currently have on your phone and then odin flash in, if your problem is caused by some error in the system , this should fix it , but i am not sure ...
REMEMBER, in both cases , you will LOSE your warranty (as flash recovery or firmware will trigger KNOX) ! , think clearly before you do it . and most important of all , make a Nandroid backup , that will, at least, restore back to your current situation instead of lose anything.
if my words are useful or helpful to you , i will appreciate it you click thanks button
Nexus S GT-I9023 (died due to BOOTLOADER error / 12 months) ---> Galaxy Nexus GT-I9250 (accidentally and sadly lost / 2 months) ---> Galaxy S III GT-I9300 (be robbed, thanks to the Fuc.king Spanish Public Order !!! 2 months ) ---> Galaxy Ace GT-S5830 ---> Galaxy S III GT-I9300 (second one , hope won't get robbed again !!!)