My iphone 3GS wont activate after i updated it to IOS 6.1?

So i bought a second hand iphone 3Gs and i updated it from 4.1 to 6.1 but now it wont activate i have no clue why and I would like to know what to do.So what do I do?
>>> My iphone 3GS wont activate after i updated it to IOS 6.1?