hey
i Cannot jailbreak iphone 3gs with firmeware 4.2.1 with redsnow
i tryed redsn0w redsn0w_win_0.9.6b5 and redsn0w_win_0.9.6rc8
i upgrate the modem to 6.15.00
I do everything right its not the first time
I see the hack working See the hard drive logo when he jailbreaking
bout the iphone always comes back to recovery mode and i see the cable with itunes logo
i tryed to use the option just boot tethered right now But that does not help too

its iphone 3gs ! i tryed 2 difrrent iphones and 2 diffrent computers.. somone can help me please?

What did you answer when it asked you about new or old bootrom? Have you checked this?

Are you using redsn0w with the 4.2.1 3GS IPSW (download link here http://www.hackint0sh.org/f127/22056.htm ) when you jailbroke and when you "just boot tethered"? Redsn0w only needs the iPad IPSW to update the baseband.

Have you read http://www.hackint0sh.org/f204/196391.htm and understood the implications?