How to fix dummy output in Ubuntu

Two weeks ago I tried to dual boot my Dell Inspiron 15 5000 with a Ubuntu 16. It works well for the most part although occasionally the sound system doesn't work and Linux just shows a "Dummy output." For the most part I could fix it by restarting.

However this morning, my Ubuntu keeps showing "Dummy Output" even after restarting multiple times and now my Windows 10 has a "No Audio Output Device Installed."

I tried multiple solutions such as dealing with pulseaudio and alsa-base but none worked. Can someone explain why my Ubuntu isn't working?