v1.5 CS problem: can't connect. Attempts fail after 4 retries.

[Jeff7]

That's what it tells me - it can tell me the full info of any of the servers I view, but I can't actually connect to play. It's not the firewall either; it records no intrusion attempts at all, and my router has never been a problem for CS. I can ping the servers just fine; I can even send and receive messages to their 27015 port using an application I have. CS can't seem to establish a connection. I've also installed the Half-Life 1.1.1.0 patch.