Ok, so you might have restored your iphone 3gs using 4.3.3 ofw(official firmware) or cfw(custom firmware) using sn0wbreeze and also it might went into DFU mode loop. NOT recovery. All there could be a black screen.
I had also faced the problem problem with my 3GS. And I fixed it using redsnow beta 0.9.10b3.
Here is the stepwise description of the fix:
That's all! Now Jailbreak the device using the same version of Red Snow.
Follow the printed instructions. And here you go with your device jailbreaked. :) Now unlock it using ultrasn0w using this guide http://iguidespot.blogspot.com/2012/01/how-to-unlock-iphone-3gs-firmware-433.html.
Labels: iphone, iphone 3gs stucked dfu, iphone apps, iphone developers