GMOD crashes when joining any server

[lhughes]

Hi there,
I have googled around everywhere for this problem, and have not found any kind of fix.
Whenever I try to join a GMOD server, the game freezes. I get no error messages, hl2.exe just stops responding.
I have tried everything, I have reinstalled GMOD, deleted my entire Steam folder and reinstalled everything, verified the integrity of the game cache, deleted and unsubscribed from all my addons, run in compatibility mode.
I don't think it could be a network problem because I've tried switching routers, forwarding ports, checked my firewall etc just in case.

The hardware I'm running is:
[I]
Asus M5A97 PRO - Mobo

AMD FX4100 - CPU

Nvidia GeForce GTX 550 Ti - GPU

8GB Corsair XMS3 - RAM[/I]

But I can't see how the hardware would make a difference because it runs fine in singleplayer and has always run fine in the past on both singleplayer and multiplayer. I'm running Windows 7 Ultimate 64-bit.

The game also crashes if I try to start a multiplayer game from my client, anything related to multiplayer crashes.

I have HL2, TF2 and CS:S all installed.

Any help would be hugely appreciated, as I have made no progress since yesterday when I first discovered the problem.