Have you tried installing the original ROM again?
I am in desperate need of help as I really need the phone in the next week. I am sure most of you are familiar with this problem, I'm not the first one, neither the last one to experience it. I am just going to say what happened, just in case.
Okay, well it was working perfectly fine until today, about 3pm; I had done nothing wrong. I have downloaded the new game Dungeon Hunter 4 or something like that and then played it for about 10 minutes give or take. Then I killed the application and didn't touch my phone for about half an hour. I was about to check the time and weather when I realized that my phone was stuck in this weird state which usually appears when you turn on your phone; with the Galaxy S3 screen logo. I could not turn it of so my first instinct was to pull out the battery, so I did. I tried to turn on the phone but it got stuck at the same point. Then I said to myself maybe it was the battery was not charged enough so I plugged in the cable. It opened to the battery screen which usually loads for a few seconds and then stars charging but this time it didn't; it was stuck in the loading mode.
I started to google it and see what causes this and how to solve it. I have tried most of the things but it seems as if all odds are against me. The home+vol-up+power wouldn't get me into recovery mode and it would only turn on the phone to the logo thingy. The home+vol-down+power would take me into download mode or whatever; so I tried Kies. It didn't work because at the end of the processing bit it would give me a message saying that the device was not recognized or something like that; therefore it would guide me through some other steps that I couldn't perform because I couldn't turn on the phone.
What is there left to do as I don't have any ideas left and I don't want to mess up the phone somehow; it is not rooted or anything, I had the original firmware on it.