I recently had the same issue......heres step by step:
1. with the battery OUT, grab the usb and plug into phone and computer
2 press volume down, power, and home at the same time.you should be in download mode at this point, and just press volume up to get into download mode.
3. open kies. and at this point you'd want to restore back sto stock as follows:
4. go to tools, firmware upgrade and intialisation
5. follow the on screen direction and then just wait.
6. if you want to re root, then feel free to once the phone is up and running.
i have tried this method so many times and hasnt failed me yet. IF this has helped anyone, please press the thank you button!