iPhone keep on re-starting after reset & erase

[hkg2003]

I have an original iPhone and wants to sell it to a friend. I then reset the iPhone by erase all content on it, the reset process took a long time to complete. The iPhone then goes into a re-starting process the switch off (for a second or so) and restart again...and again. I can switch off by holding the home button and the top main switch for around 10 second but the restart cycle just continue after I turn it on. What can I do now ?? Please help !

This iPhone has been unlocked and jail break and is running os ver 2.2.1.

Thanks

Henry