Other things to look at, short of performing a system recovery or a Windows reset, are check the BIOS to make sure audio is not turned off. Some versions of Windows allow you to perform a reset without affecting your data. If there is a software problem, then it could be on the Windows level. It is troubling that the Windows native (High Definition Audio Device) driver will not install in lieu of the Realtek driver. One reason that a driver will not install is hardware failure. Have you tried using Windows System Restore yet, to try to undo possible changes to the system's configuration that could have caused the driver to disappear and make it impossible to install a new driver? The link you put in your first post goes to the XPS 元21 support page, so you might want to check that you are getting the correct Realtek driver.