Source mods don't show up in my library

[Suurmestari]

Hi, I recently downloaded a source mod (Nightmare House 2 to be exact) and tried to install it. I followed the installatation instructions in the README file. (Extract the mod folder into the sourcemods folder)

However, after restarting Steam, the mod doesn't show up in my library. I have the files in Steam/steamapps/sourcemods/NH and I do have a gameinfo.txt. I have Half-Life 2 and both episodes, (even though the mod doesn't require any source based games anymore) I have Source SDK, Source SDK Base 2006, Source SDK Base 2007 and Source SDK Base 2013 Singleplayer installed.

Thanks in advance for any help!

EDIT: also, I have all my Steam games installed in an external hard disk.

[wuddih]

some mods will not show up in steam library and have to be accessed over their shortcut.

[Silicon Vampire]

http://steamcommunity.com/discussions/#games