Another shot in the dark: Have you recently upgraded your Firewall protection, if so does the Links.exe file have permission to access the Internet
I just had McAfee change their security center and I needed to add a lot of programs to the list.
After the install it only allowed about 6 programs to access the internet.
(don't know why matchmaker would work but not let you in the normal game?)
edit: I havn't used matchmaker or tried to, so I'm of no use to any answers about matchmaker