It would seem to me that you have Windows also set to use the ASIO drivers of your audio interface, and the ASIO specs seem to be created so that only a single application can access the ASIO drivers at one time.
SO, if you are happily cruising along in Sonar and a Windows sound is played (file opening, mouse clicks, whatever), or you try running Windows Media Player or playing a YouTube video, then conflict can and does occur.
I used to have that issue - but I now happen to use HDTV's for display monitors for my computers, and the HDMI cable transmits HD audio and video to the TV's speakers, if you set the Windows Default Audio Device to an HDMI port, or your on-board sound chip/card.
The above leaves only Sonar (and/or other music applications where you would want to run the audio conversions through your audio interface's ASIO drivers) as the program(s) that process through the audio interface - Windows will then never conflict with any other applications using the interface.
Splitting Windows away from accessing my audio interface ASIO drivers has made it probably 5-7 years since I have had any sort of conflict with my audio interface and anything else.
Bob Bone