artifacts on screen when playing games

[hurricane123]

What is the likely cause when playing a game,and i get artifacts(lines on the screen going off at different angles,but you can still see the actual picture through the lines)when i mostly have explosions going on in the game,but it is okay mostly when playing the game normaly.
Could it be the v/c heating up,CPU,or the v/c mem,im just guessing here?
Its my friends comp that is doing this,so i have no details of his comp.
Just would like an opinion on what would tend to cause these lines to appear when the game gets a lot of action.
Thanks.

 

[Dutch Guy]

Core overclocked too high or overheating is my first guess.
My second guess is driver errors.

 

[Phatzy]

its your memory on the card, underclock the memory and see how that goes

 

[FrenchTart]

its your memory on the card, underclock the memory and see how that goes

Sounds like this more than a core issue to me. Though with shaders being overclocked too much it's sometimes similar.