Im using my TV as a monitor but no sound is coming through it?

ive hooked up my pc to a normal monitor before and the monitor had built iin speakers and sound came through the speakers. so using the same cable i plugged my pc into my TV, but no sound is coming through my TV. my TV sound works as on YPbr and AV or w/e my TV has sound. but for my PC theres nothing? how can i change this, i really want to have sound coming through my TV?