Can't restore iPhone 4.

Hello.

My friend just bought an used iPhone 4 and he wanted to restore it. So we plug in the iPhone and pressed the restore button in the interface section for the iPhone. Meanwhile it was restoring my friend accidently plugged the iPhone out and now we are stucked.

Well we think the iPhone are missing some important files because when you plug in the iPhone to iTunes, ain't we able to see any option in the interface section for the iPhone and we can only get through the first 3 steps when you power on the iPhone (Choosing language, choosing country and then wi-fi). And the 4th step, it says "we're sorry, we are unable to..." The last of the sentence is not visible.

I wonder if anyone have any idéa to how I can fix this phone?

Thank you very much. 🙂