Won't work because I don't have a "source"

Ok, so I run garrys mod and it says I need a source game.

Ok, no problem. I look at the list of source games, and PORTAL is one of them.

I downloaded portal and it says I don’t have a source game.

Help me?

EDIT: i downloaded portal BEFORE garrys mod if that helps.

From the store page.

[editline]05:05PM[/editline]

To clarify: I’m assuming you got it from the free deal.

I got portal from the free deal.

I got it for FREE.

It means i OWN it.

That means it fits the requirement, and it doesn’t work.

http://www.facepunch.com/showthread.php?t=938836

No. While you may own it now, free source games (such as HL2DM as part of that Nvidia deal) do not have the Source SDK included.

If you want, you can get HL2DM for $5 or Half Life 2 for its discounted price. Both of those will get you what you need.