Reset my iPad, but required different Apple ID to activate

So on Monday morning, my iPad2 started messing up. It keeps shutting down and turning on. I went to best buy after school to trying to get help. Becuase I bought it right there. And they told me to reset it up. It actually fixed the problem, and then when I turn it on , it asks me my activation code, but what it shows is different than my Apple ID. I'm pretty sure they sold me an used one, even though I bought it as brand new. I went back again, and they told me have no idea what to do. Would you please tell me how to activate that iPad ? I like it so much !

<Email Edited By Host>