Can't mount certain games on Garry's Mod 13.

I have Valve Complete Pack and Garry’s Mod, with all the games already installed, and I recently re-installed Steam to fix a bunch of glitches, like Portal 2’s Co-op not working and stuff, and re-installed all my games and SDKs and Dedicated Servers, and… EVERYTHING, and I still can’t mount Counter-Strike: Source, Left 4 Dead, or some other games. I can mount “Counter-Strike: Source”, “Day of Defeat”, “Half-Life Deathmatch Source”, “Half-Life: Source”, or “Left 4 Dead”. And it won’t let me mount a mod called “Xeno Clash”. But it does let me mount “Age of Chivalry”, “D.I.P.R.I.P.”, “Dystopia”, “Half-Life 2”, “Half-Life 2: Deathmatch”, “Half-Life 2: Episode One”, “Half-Life 2: Episode Two”, “Half-Life 2: Lost Coast”, “Insurgency”, “Pirates, Vikings and Knights II”, “Portal”, “Team Fortress 2”, and “Zombie Panic! Source”. Can someone please help me figure out how to make other games compatible, including the listed games that shows a red X instead of a check-mark box, and also unlisted games like “Alien Swarm” and “Counter-Strike: Global Offensive” and other games that are supposed to be compatible with Gmod but isn’t for me due to glitches? I would appreciate the help a lot. Thanks. :smiley:

And I have Windows 7, 10 gigs of RAM, a 1.5 terabyte hard drive, an AMD processor with 3.30 GHz, an i7 core, a Beats Audio sound card, an NVIDIA GeForce GT520 video card, and all of this is on an HP Pavilion HPE PC.

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