It's weird. The problem is gone for now. I noticed that it comes and goes. Mostly though for the past few days I couldn't get in. Before that I could always connect.
Well as I mentioned above, I didn't change anything since when it was working for me. I have the same AV, same everything!
EDIT: I think something's up with 4D1 in general ATM. Even the forum pages are taking forever to load!
I don't have a router. I'm using a modem and it works for all my online games/shooters. It doesn't have a firewall. It's not blocked by windows firewall either.
IW5M used to work for me before. Now it doesn't. Nothing about my hardware, software or connection has changed. All I get when I try to get the server listing is "Connecting to online services..." and it stays there forever. I've tried all the fixes suggested in other posts but nothing works. Is this a problem at the 4D1 end or have I missed some sort of Steam update or something?