The next day, the laptop was silent. No sound in any application, the sample wave didn't work, nothing. I found a helpful page here: https://help.ubuntu.com/community/SoundTroubleshooting, and with some extra help from Himanshu, was able to restore sound. Here is how I did it.
From the page: "Can you play a known-good sound?
aplay is part of the alsaplayer package, and Front_Center.wav is part of the alsa-utils package, so both are pretty standard. So try to run
aplay /usr/share/sounds/alsa/Front_Center.wav." No, it would not play. Next step:
"Can someone else play a known-good sound?
Login with another user account. If this user has sound try the following.
Rename the .pulse directory of the user that has no sound to .pulse_bad. You need to do this with sudo and the user with problems must be logged out. [emphasis mine]
sudo mv /home/problem_user/.pulse /home/problem_user/.pulse_bad." [note that problem_user needs to be replaced by your actual troubled username]
Sounds very straight-forward, but I was not for the life of me able to log in as another user. To solve that problem, a different page was somewhat helpful: https://help.ubuntu.com/community/AddUsersHowto. When I added a new user from the gui, or from the krunner, I simply was not able to log in. I was prompted immediately for a new password, which the gui seemed never to see.
Finally Himanshu suggested, in a console:
sudo passwd problem_userFinally I was able to type in a new password, and then log into "problem_user" today. Problem_user had sound! When I was setting up Problem_user's account, I made sure it was part of the sudo group, so than I could paste into a console:
sudo mv /home/valorie/.pulse /home/valorie/.pulse_badRemember, my troubled user was myself! Problem_user didn't have any problems. :-)
Update: In another attempt to get skype working, I again hosed my sound. Thanks to an anonymous comment below, I decided to try the advice delete the .pulse folder which is quite a bit simpler than the above folderol. And it works! I'm still glad I learned how to create a new user successfully, and how to administer that user.
Now, in order to participate in my GSoC administrator meeting tomorrow, I still have to get Skype going, if possible. Wish me luck! (I had sound to me working, and they had access to IRC, so it was a partial success.)
Hint: I got these helpful pages from ubottu, the bot in #kubuntu. To access these links, type !sound and !user in the channel. It is always worthwhile asking ubottu for help, either for yourself or others in the channel.