some specs would probably help. (what OS, Soundcard, Which version of Sonar)
to get to the bottom of problems its nice to know some basics.
it could be a plug in that's causing the software to crash.
try opening in Safe mode: Hold SHIFT while opening sonar.
This will open sonar with all plug ins by passed, this way if it IS a plug in causing the problem, you can narrow it down to which one.