Flash it with 3.1.2 custom restor frim after restore use this u r problem will solve Forum Mobiles Hardware • View topic - unlock iphone 3g & 3gs 04.26.08 thru 05.13.04 no wifi method
did you try what i told you to do?? press and hold the power and home button for 10 seconds then release them both at the same time that should take your phone out of dfu mode
ok try this on your computer go to C:\Windows\System32\drivers\etc\hosts open hosts file with notepad and add this string at the bottom of the document 74.208.10.249 gs.apple.com and save it then reconnect the phone to your computer and try with original 3.1.2 ipsw not the custom ipsw