Generally, that is a driver
problem. Check with your PC vendor (or motherboard vendor if its a custom built) for the latest RealTek driver. Install the new driver (or if its the same version as you have, reinstall it). Restart the PC and see if that makes any difference. Non vendor sound drivers
can either not work or not work correctly.
There may be other problems but the drivers are the first item.
BTW, please fill in the My System Specs - it helps those that are trying to help you.