Windows 10?
In any case, right click the small speaker icon usually located right lower corner of the screen.
Look for Playback devices and Recording devices. Windows 10 has changed things around some so you may need to dig a bit more.
Overall there are quite of number of windows, tabs, and properties used to control and configure audio.
And there may be third party software involved with respect to your sound card or some utility apps.
Explore the windows, tabs, properties, etc. to determine if some configuration setting returned to some non-functional (in your case) default setting.
Look, keep some notes, and then try changing some setting (one setting at a time) to get things back to normal.
It will take some time and patience.