Just remove the battery and ofcourse the usb cable.
Just wait for about 5 minutes.
Than put the battery back in en go to recovery mode and do a factoryreset and partitionwipe.
If that's not working, do the same thing over again and than try a new flash.
What whent wrong?
Could be a lot of things.
Faulty cableconnection/ kies running in the background ( or sommething else what try to use the usbconnection.
Better is to leave the computer alone during flashing, go for a walk or tiese you gf..............