I recently jailbroke my iPhone 3G on 3.1 using blackra1n. I installed cydia, and then I deleted blackra1n. Now when I open Cydia, it closes as soon as I open it. I can't restore the phone and rejailbreak because it'll update to 4.2, and I wouldn't know how to jailbreak a phone on 4.2. I heard there's a way to fix cydia with cyberduck, but I have no clue what cyberduck is. I know it's a type of software, but I don't know where to download it, or how to fix cydia with it. I have a mac by the way.