I had a similar problem as this person. Namely, I tried to install a Realtek audio driver and my laptop could no longer find my audio card. I followed the solution given in the post I linked, but no luck. I've also uninstalled and reinstalled the ALSA mixer, but no luck there either.
The full alsa report is here.
Based on the troubleshooting guide Ubuntu has, it seems like I'm missing the driver I need. But that doesn't make sense to me because I know I had this driver before. And I also can't find the driver I would need on the Alsa site. When I look at the report for what audio card I have, I get the following:
Audio device: Intel Corporation Xeon E3-1200 v3/4th Gen Core Processor HD Audio Controller (rev 06) Subsystem: Hewlett-Packard Company Device 1962 Flags: bus master, fast devsel, latency 0, IRQ 7 Memory at b2710000 (64-bit, non-prefetchable) [size=16K] Capabilities:
00:1b.0 Audio device: Intel Corporation 8 Series/C220 Series Chipset High Definition Audio Controller (rev 04) Subsystem: Hewlett-Packard Company Device 1962 Flags: bus master, fast devsel, latency 0, IRQ 10 Memory at b2714000 (64-bit, non-prefetchable) [size=16K] Capabilities:
I can't find anything matching either of those here. This is bizarre since I know I had this driver before.