Have you tried to simply take out your SIM and put it back in again? You might try that taking out the SIM, rebooting the phone, and inserting the SIM card again.
Otherwise, you are using the correct firmware and baseband thus I am not sure why you would have no signal.
Also, I am gonna' give you a link below which is a tutorial for WinPwn (assuming you're using a PC and not a MAC). Follow that tutorial and you should be good to go.
iClarified - iPhone - How to Unlock Your iPhone With WinPwn [Updated]
However, if you have any questions after following the tutorial or something you don't understand, ask us.
Hope that helps...