Starting problem help!

I just got Garry’s Mod for few days ago.
I have treid almost everything, but whenever I try to start the game this happens:
I open it, it says “Loading…”
then it says “Creating Render Targets”
after that, I get an error message that says “The instruction at “0x00010100” referenced memory at “0xffffffff” The memory could not be read.”

I don’t know why it happens or how to fix it…

Does anyone knows why/how?

P.S. I’m not “exelent” at english, so I apologize if I’d spelled/typed something wrong.