Renewing your IP address and flushing your DNS cache can often help resolve connection issues.
For Windows:
1. Click Start then Run
2. Type cmd in the run box and press Enter (a Command Console window should appear)
3. In the Command Console window, type ipconfig /release and press Enter
4. Wait for a few seconds for a reply that the IP address has been released
5. In the Command Console window, type ipconfig /renew and press Enter
6. Wait for a few seconds for a reply that the IP address has been re-established
7. In the Command Console window, type ipconfig/flushdns and press Enter
8. Close the Command Console window and attempt to play the game
For Macintosh Apple OS-X:
1. Click Apple, then System Preferences, then Network and finally Network Status
2. Select Built-in Ethernet from the Network Status menu and click Configure
3. Click Renew DHCP Lease (this process may take a few minutes)
4. Close the Network Status window
5. Open the Terminal
* If using Mac OSX 10.4 or earlier, type lookupd -flushcache
* If using Mac OSX 10.5, type dscacheutil -flushcache