i got an iPhone 3G,and it ran 4.2.1,so i got 3.1.2 on it,and THEN,LATER i Jailbroke it,using blackra1n on my mac,then i did it!
i hit settings>general>Reset>Erase all data and factory reset! i ended up getting a combination Apple Logo+Spinning Wheel. i REALLY NEED THIS FIXED,with NO POWER...