I am in the same position. I have followed everything up to "./fastboot reboot", and my Kindle 4 NT wont boot at all. I have read elsewhere on the forum that this could be caused by a "discharged battery" or the diag partition being written to incorrectly (mismatched version possibly?). The md5sum matched those in the script. I'm letting my kindle charge, and will try later. I would like to know others' thoughts about this.