Symptoms: Cannot unmute sound or turn up volume in Windows 7. Resolution: If you cannot unmute sound in Windows 7, most likely this is a driver issue.
To fix sound not being able to be turned up or unmuted, reinstall or update your sound card driver. If this doesn’t work, perhaps you’ve plugged your speakers into the motherboard’s sound card (if you have two sound cards). Ensure the cables are connected correctly, otherwise you may have a hardware issue.