We have to try and eliminate possible problem areas
Let's look at the FireWire card as a possible issue.
Don't connect the FireWire cable to your audio device. That eliminates the audio device and the FireWire card.
If you have a Sonar project with just recorded audio. Load it. Change your audio setting to MME drivers. Remember we want to get Sonar running even if poorly. Make sure to reroute all you outputs to the correct device and see if Sonar runs.
If it does it tells you that there is an issue with the FireWire card.
Also another thing I've not seen mentioned is Windows updates. Make sure to do them all. Not optional but recommended ones. This may require several goes and reboots before you get them all. I've had occasions where a windows update has caused Sonar not to run but not for quite a while.
I would do the eliminate the FireWire card first, but do the windows update anyway regardless of the outcome.