Basically, this is a hardware problem. Are you familiar with “sudden death?” Well, this is one version of it. I’ve talked with an authorized Samsung tech last year regarding this issue and according to him the problem is with the eMMC controller getting busted.
This is a problem you can’t fix on your own and if you want it fixed, you need to have an expert tech to take a look at the phone.
Read more at http://thedroidguy.com/2014/08/samsung-galaxy-s3-user-problems-fix-part-32-96684#ekVMOVUqC43Xw5hK.99