Alienware m15x graphics card

Hey guys.. I m in a troubletrouble since  my alienware m15x 720q gtx 260m is not starting and just showing dim lights on pressing power button. After going to repair the guy is saying the graphics card is shot. I want to know the possible reasons my graphics card broke and wat is the solution. I mean if someone can repair or i have to go for a new one. If new which one is cheap and gud coz i dont wana spend too much for this old beast