Sound dissappears

Hi,
I have a very frustrating problem. The sound from my pc will work great one
moment just to completely dissappear the next. I've had vista for more than a
half year without any sound issues, but about two weeks ago this problem
started. At first I figured it was a problem with the onboard sound, and
decided to buy a regular soundcard (creative x-fi xtrememusic). The problem
continues however.

The sound works fine right after driver installation, but at some point
within the next 24 hours it will suddenly dissappear without any apparent
reason. It has happened when I was listening to music or watching tv with
nothing else running in the background. Sometimes the sound will come back
just as suddenly as it has gone, but it can take hours and seems to be just
as random as when it goes. Restarting the computer sometimes helps but most
often doesn't.

I have installed the newest drivers to every piece of hardware and every
update to Vista (not SP1-RC1), and have also tried to do a complete reinstall
of vista with a clean harddrive, but the problem persists.

I have looked in the eventlog but can find nothing that looks to be related.
There are no reports of error or any other visual sign of there being a
problem.

Any suggestions or help is appreciated.