I think you've covered all the stuff I'd try and have encountered so far. I guess you can try to remove the sound card from YaST and reinstall/reconfigure and see if that helps. I take it you've done an online update already and all your s/w is up to date. If you haven't do that first since I know that alsa and arts have been updated within the last two weeks or so.
So I guess in summary try to:
1. Update all s/w related to sound via OnLine Update
2. Remove from YaST your soundcard and then reprobe/reinstall via YaST. (check volume levels)
3. Check and see if card works.
4. Is your user a member of the audio group?
If the card still doesn't work you may need to go google crazy and search for specifics about your card and the error.
Abisko00 had suggested installing esound. I haven't used this app to my knowledge, but I know from reading post here that the advise he offers is wise to take.
I did have a problem once and I couldn't recreate it after I fixed it, but I noticed that if I had amaroK loaded, whether it was playing music or not, no other system sounds would work. I'm not even sure how I fixed it so I'm assuming an OnLine update took care of it.
I had some free time to do some searching. Here's an article that may explain what you're experiencing. You stated that only certain apps have sounds and this has enlightened me too.