Not that it matters, but what version were you on before?
In any case, find your AUD.INI file and
move it someplace where Sonar can't see it. Restart Sonar and let it find your audio interface again. If you are using anything other than ASIO, you should re-profile your interface in Sonar. Even if you
are using ASIO, it can help to switch to a different mode, reprofile, then switch back to ASIO. If it all goes south, just put your old AUD.INI back and you'll be back where you started.
Another thing to check is for latency caused by your PC. Download and run LatencyMon and it will tell you if it finds any big issues.
Regards,
Dan