Greetings
I have had some similar recent nonsense that my paranoia attributes to ever more systemd convenience junk, but wait...I'll resist the urge to rant.
It used to be that the best if not the only way to fix hardware issues was from command line. But we should admit that even the most leet admin spends some, if not most time in X these days on his desktop or laptop, even if a console is constantly open.
It is still worthwhile to go through the typical
Code:
cat /proc/asound/cards
------- and --------
aplay -D default /usr/share/sounds/alsa/Front_Center.wav
if nothing more than to see what errors you receive. That said, there is so much on top of the base once in X anymore it is also wise to seek information and testing within it, since I'm guessing you're not all that concerned about sound on runlevel 3.
If you're using some Gnome derivative, I can't help much. I've just never liked it. I love Xfce4 but it does seem to lack some utility of KDE, and especially in this area. In KDE, one can launch the "System Settings" app and scroll to "Multimedia" and open it. In there is Phonon, which has a list of detected cards and it is common that "here today, gone tomorrow" sound is caused by conflicts, lately by HDMI sound aboard video cards.
You can select each detected item from the list and hit the "Test" button to see if you hear anything. I know, not nearly as cool as actual error messages, but it is the bottom line after all.
If you have KDE and do this and see multiple entries, especially for any HDA or HDMI devices you are going to either have to blacklist them or write a very specific "~/.asoundrc" that will implement reasonable sharing of duties.
At this point I should probably shutup and let you find out what's going on and wait to hear back. Hope this helps some.