You cant just tell someone not to play a game. Especially if its a cool game.
You problem definately sounds like a hardware mishap to me. If you over-overclock your graphics card than you defianately get some artifacts that pop up here and there.
If your laptop is considerable old and if you are tech savy and feel that you can open your case without kiling something you may want to do that. Get an airduster and clean that sucker out. Hopefully something as simple as that will fix the problem.
If that doesnt work dial up toshibas number and demand they replace the graphics card. Hopefully its not sodered on or integrated into the motherboard.