it seems this issue isn't just with line6 ux2 but many other audio interfaces
http://answers.microsoft.com/en-us/windows/forum/windows_7-pictures/audio-stops-working-but-works-after-a-reboot/f3684f19-ee21-4e90-ae4c-98acb797d019?page=9&tm=1368283692511#LastReply
http://www.sevenforums.com/gaming/188362-sound-suddenly-stops-during-gaming.html#post2394416
its hard to tell what's causing it driver, usb, power issue, ect.
hopefully this will work: thanks "Just Startin'" The solution: 1. open power options. 2. click "change plan settings" for the plan you are currently using 3. Click "change advanced power settings" 4. Under USB settings -->USB selective suspend setting --> setting, change to disabled
