I had a very similar problem in that the Volume was being muted everytime I
rebooted. Here is how I solved it.
First go to Start..Accessories ...Entertainment... Volume Control
Open that and make sure nothing is muted. I then maximized all the Volumes
except for Player control... that I set at about 75%
My sound card is Soundblaster and on the Windows Update page are new drivers
for Creative Labs. I installed those new drivers and it cured the problem.