I also had a defective firmware upgrade but I kept the GT connected to kies so when I click the emergency firmware recovery,my gt showed up with an "number" to be able to do a recovery.
Try to connect to kies, go to emergency firmware recovery and see if your GT shows up in the list.
Otherwise also try the power button-volume up button factory reset procedure while the GT is off.
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I also had a defective firmware upgrade but I kept the GT connected to kies so when I click the emergency firmware recovery,my gt showed up with an "number" to be able to do a recovery.
Try to connect to kies, go to emergency firmware recovery and see if your GT shows up in the list.
Otherwise also try the power button-volume up button factory reset procedure while the GT is off.
Best of luck to you....
Good luck
Kies Emergency Recovery Code