Did you mount it to the addons folder in garrys mod's files?
Are all of the games installed?I have downloaded all the addons.
I Have bought all hl2 games (hl1, hl2, hl2ep1, hl2ep2)
I Have CSS.
Are all of the games installed?
Have you mounted the games on your GMod aswell, which you can do from the main menu?