With the greatest respect to people, I think there is a habit of attributing problems to the wrong causes, and then superstitions build up around those associations. Yes, sometimes merely installing software does leave it running in the background. And yes, software running in the background can take up memory and CPU time which may slow down your computer's performance. But generally speaking, other non-audio software is not going to change your audio drivers, it's not going to change your MIDI or audio inputs or outputs, and it has no way of inspiring plugins or Sonar to crash. I have myself experienced the rare occasion where another piece of software was legitimately affecting my Sonar use - and that was because it is a rare piece of software that does something quite specific with the graphics hardware. I have a ton of other things running (including things I would recommend others switch off, just to put people's mind at ease) and nothing interferes.
 
And sometimes, I think people bring it upon themselves by taking the superstition too far. "I leave my PC disconnected from the internet at all times, except every 6 months I reconnect it to download Sonar updates". Don't do that. Most likely you're suffering with broken or suboptimal OS software during that period, sometimes including drivers for your hardware, and when you do finally connect to the internet you have months-old security flaws in the software which make you much more vulnerable to viruses than someone who is connected 24/7 but accepting security fixes as they come.
 
The main thing I would suggest for multi-purpose PCs is this. Wait until 2 or 3 minutes after you've booted up, then open up Task Manager with Ctrl-Shift-Esc. Click on the 'CPU' column, and watch for a few seconds. Note any programs that keep appearing at or near the top of that list, and ask yourself (a) Do I know what this program is? (b) Is it essential I keep the program installed? (c) Can I at least set it to not start up automatically when I boot Windows? Answer those in order, considering removing the program or making it not start when Windows does. Then click the Memory column and do the same. (On Windows 8 you can do this for Disk and Network access, too.) Taming the top handful of culprits will be a decent use of your time.

I still get problems, many of which stem from my lack of understanding a "feature of Sonar", others are bugs.
 
But I can tell you it has really made my life better to have upgraded my interface to an RME Fireface UCX. I tried the Rolands and Tascams and Midimans in the past, thinking the RME was way overpriced and unnecessary for my level. But wow what a difference in sound and reliability. At first, the RME was not working so well, but after I disabled the built in soundcard that comes on the motherboard, I got the low latency, reliable, and pro sounding computer I wanted.

I have been running cakewalk for Ohhh  10 plus years in all of its iterations  I currently run x3 and Platinum in a production environment whilst running ethernet antivirus blah blah blah etc etc.  With no problems other than the usual bugs I would look at your computer config and make adjustments to hardware and such before blaming Sonar most likely you have a poorly configured workstation not ideal for audio production If you are interested in changing that pm me 
Cheers, Dave

Sonar has Mix Recall now, so I would suggest dumbing down the mixing process.
1.Do a barebones recording/playback setup w/ tracks only, output to a Master.
2.Click the big "FX" button on the Control Bar. This will (hopefully) eliminate any
   crashes from effect plugins or VSTi output.
3.Save the mix as "Barebones" in Mix Recall(by the way, the Mix Recall dialogue
   has a lot of this functionality[fx, et al] built in).
 
Repeat the process with Sub Busses, FX on, Time Based etc.
 
Hope this helps
 
Mel