Windows 7 freeze when playing in OpenGL game

Hi! I'm new here, and I've also got a problem. Firstly, I'm from Poland so don't be angry if I'd make any grammar mistakes. I'd try to not make them ;p I've got this weird problem with my notebook. OS is Windows 7 x64 Ultimate Edition and when I'm playing in Wolfenstein Enemy Territory after 20-30 minutes of play system suddenly's going to freeze. I can hear weird sound from my headphones...