Please do try to uninstall/reinstall the Sound card driver.
- Go to Device Manager and uninstall the Realtek driver.
- Next is to download and install the latest driver from the manufacturer site of the Motherboard.
- Reboot your PC once the latest driver has been installed then test it again.
- If all these will not work, do run System Restore and bring it back to an earlier date or time when it was working properly.
- Here's how: http://windows.microsoft.com/en-ph/windows-10/windows-10-recovery-options