I have reset my iphone 4 settings, and it still won't switch on after 48 hours?

The apple sign that comes on when you switch your phone on, is constantly on the screen, I have tried plugging it in, holding the 2 buttons, it does switch off and on again but stops at the apple again. Can anyone help? I have sold it and need to post it soon!

This sis because your phone was jailbroken now you must have to restore it through iTunes.