T-Mobile Galaxy S3 - Tried to reset to factory settings. Phone not rebooting

[500words]

Ever since my (non-rooted) phone upgraded to the latest version of Android, I've been getting tons of acore errors. After reading in the forums, I backed up the device and decided to reset it to factory settings. The phone started to reboot, but got stuck on the T-Mobile 4G LTE splash screen. After waiting 30 minutes, I pulled the battery and the phone rebooted. Once again, I'm stuck at the same screen. The LED in the top left corner of the phone is on and the T-Mobile Logo is "moving" but I cannot get the phone to work. Any advice would be appreciated!

Thanks
Roy