iPhone 3G shows apple logo, then turns off

Hello. I have had my iPhone 3G 16GB (white) since last July and just recently I decided to let my brother use it because I got the 3G S.

I chose Settings, General, Reset, Erase all Content and Settings in order to get all of my stuff of there. Now, when I try to turn the phone on, it shows the apple logo for a little bit, and then shuts off. Every time I try to turn it on it does the same thing.

Any ideas as to what's wrong? I tried plugging it into the computer and the phone turns on to the apple screen, then turns off after a little longer. The device never appears in iTunes.