Monitor Goes to sleep while playing City Of Heroes

[Aphraksis]

Hi, i need some help. When i play the game City Of Heroes sometimes my computer locks up and my monitor goes to sleep. After about 30 seconds of audio looping, my compute4r unfreezes and resumes the current action. But my monitor remains off. I can hear the noises my game makes and when i type (to try and chat when monitor is off) the keystrokes make the normal noises in the games chat engine. So that means my computer is working properly. Just my monitor is off. PLEASE i need help.