What is the brand of the sound card ? You can type
$ lspci | grep Audio
Have you tried other mixers, for example "alsamixer" in console or alsamixergui ?
You say only PCM works, this might depend on the device and the driver for the device : do you have sound anyhow ?
Not tried any other mixers yet .
Yes I have sound but its only controllable with the PCM setting on the mixer .
$ lspci | grep Audio = Multimedia audio controller: Silicon Integrated Systems [SiS] SiS7012 AC'97 Sound Controller (rev a0)
Tonight I have reinstall openbox on another machine I mainly use to listen to the BBC iplayer music (in the uk).
This has the same problems eg Sys tray volume does not work then if you right click on it and open up the mixer only PCM works.
It also has another problem that I have no control of sound coming from the internal speaker which I want to turn off.
$ lspci | grep Audio = Multimedia audio controller: Intel Corporation 82801BA/BAM AC'97 Audio Controller (rev 02)
Edits details added.