I have a HP G62 laptop with windows 7 home premium and play dvds with windows media player. I have an intermittent problem with the volume decreasing. The sound simply falls to zero and it may happen when I am not even touching the keyboard.
Does a headset react the same way? Yes Is the volume control actually moving to show a decreased volume? Yes, that's what is so strange, you can see it slowly falling. Even more oddly, opening a web browser using the button on the laptop sometimes stops the fall.
Glad the volume control is moving, that means it is not a hardware issue.
I am trying to think of anything that might try to control the volume without your input. About all I can come up with is a communications device, but that will normally mute it completely.
If the problems are intermittent, it might be best to try to find something common about your system when this event occurs. If you start your system without running any other software, does it have the problem?
Do you run some game that might effect the volume?
If you can't think of anything, and you are not using Skype or something similar. You are not hitting any key combinations that would lower the volume. There is no physical control on the volume that might be turned down. Or there is not a second mixing utility that might be overriding your settings, I would think about reinstalling the audio drivers.