Cant install any addons.

Hey i have a big problem with garrys mod 11. I cant install any mods or addons or maps. i tried to add asuran gun. When in game it shows the gun i can equip it but cant shoot it shows like shooting but nothing come out from gun and it does no damage.When i tried to install stargate it even doesnt show stargate.Please help me...... Can it be because i am using Garrys mod 11 non-steam?

Garry’s Mod non-Steam is pirating. And I’m going to say yes, it is because if that.

If you illegally downloaded it, nothing will work. Immediately remove and don’t be a cheap bastard and buy it for 10 bucks.

-OR-

If you bought a CD version (which I’m pretty sure doesn’t exist, or you probably got scammed) aka you got a legit version you probably installed it incorrectly.
Post a link and tell us where you installed it to.