Recently after my system updated packages, I restarted my computer and found that sound no longer works. aplay -l and pulseaudio both report that there are no sound devices, even though they were working fine previously.
I checked and found that the proper kernel modules were not loaded. Running sudo modprobe snd_hda_intel got my motherboard's sound device to immediately show up in pulseaudio, and sudo modprobe snd_usb_audio got my USB audio devices working as well.
I haven't edited any audio configuration files recently, but I'd like to get this working automatically so that Ubuntu will load the proper kernel modules at boot time after detecting my hardware.
Ubuntu 18.04.1 with Linux 4.15.0-39-generic
Can you try reloading alsa?
In my case, alsa did know about the sound card, but the installed PulseAudio server ignored it completely. After running the command above, I had sound again.