I recently got http://us.store.creative.com/Sound-Blaster-Arena-Surround-USB-Gaming/M/B002J9HCV0.htm and sometimes I find the sound just cuts off. It seems to only do it while playing Oblivion.
I have to usually go to Windows, disable and re-enable as default sound device. Sometimes unplugging then plugging back in then quitting to main menu fixes it right there. Other times I have to go to Windows and disable>enable device.

It never goes off while watching tv shows I have downloaded.

Of course latest drivers are installed.