Hi...go into your sound options by right clicking the speaker icon in your system tray and selecting "sounds". Click on the "Recording" tab and disable any microphones that are enabled. Save settings, exit sounds and try your sound to see if that was the problem.
If not, make sure you have the most recent motherboard bios version installed. Then try again if there was a newer version available, after updating to that version.
Are you using the integrated sound, or an add in PCI soundcard?