The only thing I can think of is that either your firewall is blocking it or your ISP is blocking it. Since you are on the forums it's unlikely to be your ISP.
Try turning off your firewall, briefly, and see if you can get in then. If so, you'll need to tune up your firewall settings. DO NOT continue running without the firewall. Once you've determined whether or not that is the problem, turn it back on and figure out how to fix it from there. Running without the firewall can be dangerous.