Boot into download mode and try to connect, if okay then flash a full stock firmware.
If it still won't connect then probably the emmc chip is blown, new motherboard required.
Sent from my GT-I9300 using Tapatalk
Note: This quote doesn't automatically apply to everyone, decide for yourself if it might apply to you.
Originally Posted by justruss
What has this place become?
It's essentially a few people graciously answering the same repeating of immature, lazy, demanding questions from the masses.
Nobody searches. Nobody reads the first posts or titles of threads. Nobody even looks at posts a couple above their own.