refurbised iPad can't download IOS 7

I bought a refurbised iPad 3, and will not download the IOS 7. When I tried to download it, it was "verifying update" for 3 days, so I had to force to shut my iPad down. I have tried only once twice since IOS 7 has been available. The same thing happened the second time, only after I turned my iPad back on, it would shut down, and then turn back on, shut down, turn on. I forced my iPad to shut down again and didn't have a problem with it until yesterday. My iPad just kept turning on and off, and kept saying "unable to verify update" when I hadn't even tried to update the iPad. What is going on?