My friend has this same exact problem.
The problem is this:
His game launches normally, and gives him full access to options, the server browser, everything.
The the very moment he steps into a singleplayer game or a multiplayer server, his entire screen is black, although the game is still able to play, as he can hear the sound of himself walking and switching to different weapons. He can even connect to a server and walk around.
He has tried every google solution under the sun, including:
Verifying game cache
Reinstalling Garry’s mod
setting game configuration settings to lowest possible
setting game configuration settings to highest possible
forcing steam to run garry’s mod in direct x version 8.1
forcing steam to run garry’s mod in direct x version 7
forcing steam to run garry’s mod at a fixed resolution
Turning off Windows Aero
His specs are as followed:
Windows 7 home premium 64 bits
Intel I7-3770 CPU @ 3.40GHz 3.40GHz
16. Go RAM
Nvidia GeForce GTX 570
1 To. Hard Drive
100 Go. SSD Hard drive
Please, someone help me find a solution for my friend.