L4D2 - Sent back to lobby - No error messages - Help?

[Foshizo]

So after several weeks of troubleshooting, I finally figured why I've been having this problem;

Ever since I got a new PC + Windows 8, I can run L4D just fine and play Singleplayer, but on Campaign and Versus, I get kicked back to lobby without fail. I can always play the first level just fine, but as soon as the second or third level loads, I freeze at the loading sreen. About 5-6 minutes later, my screen goes back to the lobby. No one can see me type, the levels progress, and it seems like the game is still progressing. Checking console, I found something along the lines of:

"Server connection timed out"

However, again, I don't get any error messages or any notifications. I just get sent back to lobby. Tried verifying game cache, deleting all addons, reinstalling, disabling Windows Firewall+Antivirus, but it still seems to constantly happen on any online servers. I have no issue playing any other games online.

Anyone know what to do?

[Foshizo]

Server connection timed out.
BinkOpen( d:\program files\steam\steamapps\common\left 4 dead 2\left4dead2\media\l4d2_background01.bik )

[Myn]

^ I have the same exact problem. Did you ever get it resolved?