GMod won't launch on new rig

[chibale]

Hey there,

[b]Specs[/b]
Processor: Intel(R) Core(TM) i7-2600S CPU @ 2.80GHz (8 CPUs), ~2.8GHz
Memory: 16384MB RAM
Card name: Sapphire Radeon HD 6970 2GB
Operating System: Windows 7 Ultimate 64-bit (6.1, Build 7601) Service Pack 1

[b]Problem[/b]
On the new machine, I don't get past the loading screen, which locks up my right (main) screen in 800x600 reso (as far as I can tell) indefinitely. I let it load about an hour tops, but no change. I don't get any error messages, and it doesn't crash during that time.
It sounds exactly like problems some users had months and years back, but all those threads referred to an update that should have fixed it in the meantime.

[b]What I tried so far[/b]
I've tried fresh reinstalls of both GMod and Steam, verifying gmod gamecache + all related source games, running it on alternate user account (same result), running it with my second screen disabled, deleting gmod/gmod, reinstalling latest GPU drivers and starting it with windowed and fullscreen launch parameters (with both: application doesn't launch, hl2 process does), as well as dx81 (no change).

As far as I can tell, all drivers are up to date, and I got no available Windows updates.

Its probably gonna be something simple where I feel stupid afterwards for not noticing myself, but I'm stuck right now.

Thanks in advance!

"screenie" [url]http://dl.dropbox.com/u/21573370/Screenshots/IMG_1588.jpg[/url]

edit: updated for nicer form