Your having the same issue as I am as if you would have searched you would have found that out. It appears as of now http://www.mtabeta.com, the site/server that holds every single mta account (as so I believe) is currently down. We all have to wait, thus of us who don't have the game installed until the team decides to give us support, whenever that happens.
On a side note, this problem is NOT the serial problem. If we already have accounts then obviously we can't be having the serial problem people who don't have accounts are having. Therefore, don't worry about any issues with serials.