Hey-o!
Have you tried re-installing the game? I know that may sometimes affect the game. Also, do you have a proxy going currently? You wanna make sure that is closed or else you won't be able to enter the game.
It could possibly be something with the IP, but I am not 100% sure on how that could affect it. I'd say one of the best things for you to do if nothing else is working would be to re-install the whole game. You could back-up your files first so you don't lose anything, but I'd only do that as a last resort if you haven't done it already!
~Dirt.