Something happened to make Sonar stop working. Used SPlat all day Monday without incident until around 7pm. All of a sudden it stopped playing. Hitting the space bar and the play button does nothing. Closed everything and rebooted. Still no go. 32 bit Splat also won't play. I did nothing outside of Sonar except browse the internet on occasion.

Check the timing masters in Preferences > Audio > Driver Settings

soens
I did nothing outside of Sonar except browse the internet on occasion.

This may have taken over your audio. For example if I open Chrome to a site that defaults to playing sound, then SONAR usually won't respond until I quit Chrome.
 
scook's advice is, as usual, excellent.

I get that, but this was a totally new thing. The next day it worked as usual. I think it may have been a memory issue with Sonar.