Please ensure that osu! is allowed full access in whatever firewall or anti-virus software you may be using - internet connectivity is required to log into our game servers.
Even if your firewall policy allows other games through without adding exceptions, try adding one for osu! - it'll probably help!
If you're still having issues connecting to our game servers, please submit a support ticket containing a tracert cho.ppy.sh output log (see
here for information on how to do this).