'Unable to connect' means you're either typing in the wrong username or password.
If you have typed the wrong username or password too many times, your IP gets a 10-15 minute suspension.
To verify if your account is actually banned, login to your account at
http://en.nostalrius.org/ and it will tell you the status of your account.
Otherwise, please read the sticky (
https://forum.nostalrius.org/viewtopic.php?f=45&t=11569 ) for connectivity problems. It will most likely have your issue in there.