I seem to have stumbled upon a possible solution to the login problems.
I started using gamebooster a few days ago to increase my fps in games. When I used it in crysis 2, i realized i was able to login finally. My only guess is that gamebooster disabled something that was clashing with my logging in. I used it on my friends pc as well and he too was able to login after that.
Well this solution may or may not work for you but you can give it a go.
Here's the link
http://www.iobit.com/gamebooster.html
Cheers!!