Toshiba Satellite Sound quits

Up until about 2 weeks ago, everything was working properly. Now, the sound works for varying lengths of time, then quits. This issue only affects the internal speakers; if I am using the HDMI to play audio, it is unaffected. I have tried everything I know, up to and including a fresh install.

the particulars:
Ubuntu 12.10
Toshiba Satellite L755-S5167
Bluetooth Dongle (for external keyboard and mouse when using HDMI)
External WD MyBook 2TB USB HDD

The sound works under Win7. It also works under Knoppix LiveDVD. It does *not* work at all with Puppy Linux.

alsamixer claims the sound is working even after it quits.

Could this be something Windows 7 has done to my sound card? Some 'feature' I must turn off in Win7 so my sound will continue working?

Any help would be appreciated.

Thank you ever so for all your help. Given my experience, I'll not bother posting again.