Ensure you have the latest version that may be found here: viewtopic.php?f=59&t=37899
If you followed the guide but still can't see any servers:
- Verify that your firewall isn't blocking connections from iw5mp.exe
- Run iw5mp.exe as an administrator
- Perform a full reinstall of the game.
If none of these solutions work, it may just be that the master server ( used to get a list of all active servers ) may be down. Waiting a few hours should rectify the issue.