No "My System Specs" which can help someone to try and help you.
What is the status of the RealTek in the Device Manager? Showing an error code? Showing Working OK? In either case, RIGHT click on the entry for the RealTek and then LEFT click "Uninstall" DO NOT check the box to uninstall the drivers
. Restart the PC and when Windows starts it will detect and reinstall the sound. This fixes a lot of problems and my fix yours.