If I'm watching a video (especially if I click on the video timeline to move ahead in the video), the sound will simply stop. Not just in WMP, but the sound on the entire computer will stop until I either log off/on or restart. I have had multiple sets of speakers and this phenomenon is not necessarily limited to WMP, but that is when i notice it most often.
Adding more strangeness, when i do log off or shut down in order to restart the sound, my computer makes the "goodbye" sounds!!! it just won't play any sounds and i haven't found a way to "fool" it into thinking i'm logging off so that the sound kicks back in without doing so...