though is your firewall off or is it just deciding to work now? If it is off you should get it back on once you figure out how to lower its settings. If not, then just ignore this part.
I don't know if the problem was solved yet or not i'm to lazy to read all the comments but deadmaster had the same problem and it was because she was trying to log in to the server on a 1.7.2 client. try downgrading to 1.6.4