Sometimes the headphones do not work because the autoprobe of your sound card may not have been correctly identified at boot during the loading of the alsa kernel module. You could consider:
- carefully check your mixer, and to get better help post here the settings you have applied to your mixer and/or
- possibly force a model configuration upon boot where the mute will work, and / or
- possibly update to the latest alsa version (as openSUSE-11.1 does NOT have the latest alsa version Alsa-update - openSUSE and/or
- if your hardware of your PC is really new, then a bug report may be necessary to have the alsa kernel model updated to appropriately handle your PCs hardware
There are a lot of hints and links in the audio troubleshooting guide and you could start working thru that. If that does not help, post and after I get back from vacation (in a week or so) I can try guide you thru this in more detail.
Audio troubleshooting guide link:
SDB:AudioTroubleshooting - openSUSE