Problem with weapons textures...I think, unplayable GMod

I’ve installed the game on my desktop PC, I already have it on my laptop (and it works fine there), but when I load a map to play a solo game in sandbox all my weapons have a strange texture, like a piramid going into the sky, I tried to spawn NPC’s but they were invisible and just after I killed one of them they’ll appear with the head going the same direction as my weapon, the controls are fine (I can do everything (shooting, jumping, moving, etc…), but this texture bug (I think it must be the textures) won’t let me see anything so the game becomes unplayable.
My PC is old but I think gmod should work fine, it has:

  • Intel pentium (dual core if I’m not mistaken) 3.4 Ghz
  • 2 Gb RAM (it doesn’t say what type)
  • Intel G33/G31 Express chipset family (I think this could be the problem)
  • DirectX 9.0 installed.
    So I think that my computer should run Gmod easily.
    Do you know how to solve this problem?
    P.S. If you need a picture just ask (and tell me how to put it on here)

Try -dxlevel 81 launch parameter, if it doesn’t help, get a new video card.