Iphone stuck on Apple logo and loading circle.

Hi all!

Bought a faulty second hand iPhone :o. It came stuck in recovery mode, and while trying to restore to IOS 5.1.1 I kept getting error 1604.

I decided to restore to the current firmware (not sure if it's jailbroken or not) by downloading IOS 4.2.1 (unjailbroken). I thought this had worked as I got no error, but now it's stuck on the apple logo with the swirling loading circle :confused:

Any idea what I can do, or what is causing it?
Or is it just a hardware issue:( ?

Thanks sooo much for any help whatsoever.