I have an iPhone 4s.I want to hard restest it?

I bought an iPhone 4s and i want to hard reset it. I don't know the password and every time i try and reset it it says can't reset till passcode is enter but i can't put in the passcode. What should i do?

Chances are that you bought a stolen phone. If it's iCloud locked, it will be useless.
Put your phone in DFU mode and restore it in iTunes.
Go through the Set Up process, and if it asks for the previous owner's Apple ID to continue, you're screwed.

If it isn't iCloud locked, then you should be fine.