I've been having problems with my 3GS (New Bootrom) after upgrading it to iPad baseband and unlocking it with Ultrasn0w on 4.2.1 and then stupidly upgrading it to 4.3.1 and having a recovery loop...
I thought I'd got around it by using ultrasn0w to create a custom firmware with baseband preservation...and it was working, ie it managed to restore and it was coming up on itunes to set up, but when it starts, it won't boot! It shows the apple logo with the spinning circle of death...what can I do?