Hey guys so i was going through the forums and i saw that loads of people have been having problems with the Samsung Galaxy S3 and i came across this i also bumpt into this problem and thankfully it worked i hope this helps ( i do not take any credit for this information the credit goes to someone in the forums called meoMonares)

Finally, the solution! I made use of Samsung Kies. Here's what I did:

1. Install Samsung Kies in your computer if you don't have. (You may have to choose between Kies or Kies3. Kindly check Samsung website)
2. Connect your device to computer.
3. Turn on your device. As with our case, it will get stuck in the splash screen logo.
4. Press Volume Down + Home button + Power button. Hold it for some time until the ODIN screen is displayed. (The one with green Android character and it says "Downloading... Do not turn off the target!!")
5. Launch Samsung Kies.
6. Ignore if you see some prompts that say your device is unrecognized.
7. Go to Tool > Firmware upgrade and Initialisation
8. Enter your device's model name. (Ex: GT-I9300). Be aware of the uppercase letters.
9. Click OK.
10. Enter your S/N the click OK.
11. Then follow the succeeding instructions as it will now direct you to downloading your firmware.
12. Just wait until it's done and auto-upgrade with your device shall commence.
13. Then whoala! Welcome your device back!

This works for me. I have Galaxy S3.

Hope this helps!