have you checked the volume control go to control panel/sound and audio devices/audio tab volume failing that check your audio drivers are installed correctly control panel/ system /hardware /device manager/scroll down to sound video and game controllers is thier a circle with an exclamation mark i know the first sounds obvious but is a possibility with a new install
Have you checked your sound card via the Direct X Diagnostic tool? Go to System info, tools, Direct X Diagnostic tool. Check for sound and if it finds any problems. Check the card/sound in Control Panel also.