"Unknown error has occurred" in MacBook Air App Store

Hi,

When I try to log onto the App Store from my used MacBook Air, it says "unknown error has occured" and doesn't allow me to move forward. I have read that these typs of issues (I am having problems with logging into the computer with my Apple ID and FaceTime as well) can be fixed once upgrading to Mountain Lion, but I cannot upgrade if I cannot connect to the store.

So, how do I go about entering the store without making an alternate ID?

Thanks!