John,
Here's a link to a thread from a few years ago that has some bearing on your problem.
It seems that Audio settings changed by themselves. I wonder if this has happened to you.
To check Windows' settings....
1. Right-click on the speaker icon on the taskbar (beside the clock) and select "Playback Devices".
2. Make sure "Playback" is selected (#1), right-click on the item that has the 'default' tick next to it (#2) and select "Properties.
3. Select the "Advanced" tab (#3). Make sure the boxes labelled #4 have ticks in them and set your sound card to 16 bit 48000 kHz (44.1 is ok too).
4. Ok your way out of the windows.
Does this make a difference?
Regards,
Noel