Double check to make sure your firewall isn't blocking Sins?

Just to be sure, disable your firewall and try to connect.  (Having it disabled for a couple of minutes shouldn't have any adverse effects if all you're doing is trying to connect to ICO and not surfing around the net.)

If it connects, then for sure the firewall is your problem, you can turn it back on and figure out how to allow a program through it or post what firewall you use if you can't figure it out and the rest of us can try to point you in the right direction...

If you still have issues, turn it back on and start poking around in whatever program you have that controls application blocking.

Also just verify you're running the most recent version of the game.  You should be with a recent DD purchase but it never hurts to check and be sure.

It would really be nice if ICO displayed a more specific error message, instead of just "Disconnected from Ironclad Online" every single time.

For instance: "Internet connection not found" "Unable to resolve IP" "Disconnection due to timeout" etc.

"Disconnected from Ironclad Online" is what is displayed when you're trying to log in. The problem is not with your CD key or ICO account (most likely), but is rather with something preventing your computer from communicating with the ICO server (which verifies usernames etc, among other things).

If you have a laptop, try moving somewhere else to use a different internet connection - if trying to connect through a different ISP doesn't work either, the problem is certainly with your computer rather than with the connection.

The ICO server has been somewhat unstable the past few days though, it's crashed at least twice - you might have been unfortunate enough to have tried to log on during another downtime. However, at the time of this post, the server seems to be up and running smoothly.

If the problem still exists I could try to help you diagnose what's causing the interference on your computer.