I have a week 42 iphone 3gs that was originally on iOs 4.2.1 with baseband 05.15.04 I jailbroke it using redsn0w and upgraded the baseband to 06.15.00. Then booted it tethered to be able to install ultrasn0w from cydia. I ran ultrasn0w and everything seemed to be fine until I restarted the phone and now it won't boot. It's just stuck at the apple logo. I could try to boot it thethered again from redsn0w but I can't get it to turn off so I'm not sure I should do this as redsn0w explicitly says it should be turned off. Thank you.