Why Does My Sound Crap Out On My Computer For No Reason?

[DMark]

I boot up, log in and can hear everything just great - stream music or watch YouTube or whatever.
Then I go onto Adobe Photoshop or Illustrator or even MS Word and do some work and when I go back to the Internet to see a video or hear some music and bam - sound gone.
The only way to "fix" it is to re-boot my laptop.
Is there some reason for this?