Do a repair re-install of the SOUND drivers.
MMC seems to, sometimes, stomp all over the existing sound drivers and
registry settings.
Could be that he'll have to but if other wave sources are playing I'd start
with ATI.
I've had this happen several times and a repair install of MMC was the cure.
I've noticed on my system MMC9.13/14(at least) doesn't save its final
settings for about 8-10seconds after the program appears to have closed. I
think running another program that accesses the multimedia system before
these settings get saved can causes these problems. Maybe even just another
program. Haven't had the problem since noticing the delay but too soon to
know for sure.
Reminds me of a related story. A couple of months ago I was watching TV or
DTV and decided to edit/convert a small MPG file while watching. As soon as
Studio ran the TV screwed up. Hadn't thought about it accessing the hardware
too. A repair install got it going but still had problems after reboot.
Final solution was cleaning and reinstall like recommended at
ati.com/install. My guess is it hosed the registry.
Just observations that might help others. I could be wrong.