Audio not working, even after sound card installation

About a week ago, my computer's audio just stopped working, apropos of nothing. I tried a reboot, and after that, the green bar in the volume control began to only move a tiny bit when I click on the volume controller.

All the appropriate devices were enabled, none of the drivers seemed to be disabled or out of date, I tried re-installing the drivers, no dice, I tried updating the drivers, no dice, I tried a system restore, no dice. I even tried several different headsets, and all of them have the same issue.

Then, I decided to install a sound card, specifically, the Asus Xonar DGX, and still, there's no change at all.

What could the issue even be at this point?