iPhone 3GS stuck in recovery mode (error 21)

Hi all,

I have recently purchased an iPhone 3GS. I have fitted a new battery and tried to turn the phone on for the first time.

It is in recovery mode and when I try to restore it shows error 21. It does not show apple logo only lights up black screen towards the end of the process.

I have tried changing the hosts file on my computer but this hasn't worked.

Having only just bought the phone I have no idea if it has been jailbroken etc...

Can anyone on here help?

Thanks,

George