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There are many, many reasons why this could happen. Here are a few:
 

• Incompatible or buggy interface driver
• Hardware failure
• Windows trying to take control of your audio interface
• Missing Windows updates
• Antivirus issues

 
If the audio driver is working perfectly, it should present itself to Sonar as an ASIO (most likely, though it could be WDM) device. Sonar just makes use of that presented interface. If Windows or other software is also using the interface for audio, that could cause a conflict.
 
Regards,
Dan

As above.

Update audio interface firmware and driver.

If no joy attempt delete AUD.INI (google for details).
If not latest Sonar make sure you disable arm record monitoring in preferences.

Otherwise see if new projects are effected or not. Start in Sonar safe mode and see if you can rule out buggy 32 bit plugins...

Updating your display driver often a good idea as well.

I have the same Problem withe the Roland Quad- and also the Octa-Capture.
The same Problem is with Windows 8 and Windows 10.
Often an incompatible plugin (mostly Waves) crashes Sonar.
Then I have to restart the PC.
I had never problemes with my PCs running RME-Audio-Interfaces.
 

I have a Roland Studio-Capture and an Octa-Capture and don't have problems.
 
However, I was testing a Tascam iUR2 USB powered interface unit that only has WDM, no ASIO.  I tried starting Sonar Platinum and it came back with no devices found but would not open although it had started as the SONARPLT.exe was listed in the Task Manager.  Trying to stop it in the Task Manager was unsuccessful. 
 
I don't know how this relates to your problem, except possibly being a USB powered unit, but with the iUR2 unit Sonar was hung up.  I had to disconnect the iUR2 and that released Sonar.

Is the Quad-Capture plugged into a USB3 port?  If so, switch to USB2. 
 
Make sure you have the latest firmware/drivers for the unit.  In fact, I would do a complete uninstall/reinstall of the drivers anyway.
 
Make sure your video drivers are up to date.  Google the card to see if there is an alternative source for the drivers.  (Some versions are better than others).

I  have a Roland Octa-Capture and was having crashes with Sonar X3 under Windows 8.1 so bad I could not  complete a  single recording at all.  And during Mixing, if I added a plugin or took one away, Sonar would crash,   I though it was Sonar and was about to either give up on Sonar or move to Sonar Platinum.   Then I restored my computer to an earlier time and Sonar didn't crash any longer.   I discovered it was a Windows update that was causing the problems with Sonar.   I then restored the computer back from the original backup I made after installing Win 8.1 originally and Sonar was working well again.
 
Since then I have moved on to Windows 10 and haven't had a problem with Sonar X3e or Windows 10 at all.

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