Every time I try to play on the demo it wont let me...does anyone have any suggestions to deal with this?

Demo's over since the game is now released.

Ya demo's over and servers are down for that, but you should still be able to log in (I did Tuesday). You're probably getting the Check Network Connection error. To fix this, a probable solution is to disable internet connection sharing.... no idea why, but the full game had the same connection problems.