I'm a 2 (actually 3) monitor user.
 
I tried using just one screen for all work on a project that was giving me freeze problems across 2 screens.
The project seems much more stable...no crash at all over the usual time working.
 
I don't know your set ups...just throwing this out there for you to try if you want.  If you are using just one screen, and getting freezes anyway, I want to hear from you anyway, if you like.  If you are a two-screener getting crashes try this and let me know if you get better results...or if there is no difference.
 
Thanks. 
 
[SOLVED] My UM-3G was plugged into a  6 port USB Hub, instead of into a USB port directly in the back of the Motherboard.  All problems are now gone.  Unbelievable.  Apologies to all for wasting your time.  Richie
 

Hi. I have been using a dual monitor setup for several years with very few issues. What kind of Graphics card do you have? Is everything up to date? Which version of SONAR do you have? 
All the best.

It's no use.  Sonar froze when I was laying down markers.  Just did the June update too.  Sonar had only been open for 10 minutes.  I am now out of ideas.  I've done and tried everything, including using my studio B computer...Sonar crashes on that computer too.  But I'm using files brought over from this computer.  So the file has to be corrupted to begin with.  The only common denominator between the two computer is they are both made by HP.  The motherboards, processors, memory, midi and sound cards, usb devices, monitor screens and graphics cards are all different.  I have two very good computers, and perhaps I will list every component in both of them, but I am broken at this point.
 
I have 8 midi channels triggering 8 tracks in my Yamaha MOX6
I have one stereo audio channel for recording an acoustic guitar.
My guess is this is a midi problem with my MOX6.
My midi box is a UM-3G
The computer freezes when I press play on the spacebar, or move the cursor to a new spot on the timeline.
 
I doubt I would have these problems with all audio files.
Midi is causing the problem.
Specifically, midi coming into and out of the MOX6, and what those midi files end up looking and behaving like once they are inside Sonar.  Local control on the MOX6 is OFF.
Anyone else think this is a decent conclusion?
 

Is it always darkest...before the dawn...?
 
I re-recorded the 8 tracks from the MOX6 into Sonar in a new project.
Dropped all my markers, clicked all over the place trying to crash it.
Added back the audio track.  Rehearsed with the song for the last 3 hours.
No crashes...but I won't crow about it yet.
 
I have a feeling that my original projects, all 5 songs of an album I'm doing, were corrupted by the old hardware that I have since replaced.  I think it was one or both Hard Drives, which have both been replaced, along with the graphics card, which was swapped out with an AMD R9 380.  My original mixer (Mackie 1620 firewire) has been replaced as well (Behringer UFX1604 usb/firewire), but that was an audio problem unrelated to screen freezes.
 
I'm using just the C drive at the moment, which is a Samsung 500gb SSD.  Everything is snappy, bright, and fast, and solid.  My audio buffer setting I bumped up a little to 5ms.  This one song has been looping continuously for the last three hours.  When I go over to stop, rewind, and play and rehearse some more the computer keeps going.  This is a good sign.
 
So it looks like the original project files were corrupted.  We'll see by late tonight...because I am going to keep this thing rolling til then, or a crash...whichever comes first.

I stopped the song.  I forwarded the cursor to the END of the looped region.  I pressed play.
Crash.

have you tried updating the graphics driver ?
I don't know, your posts were some what all over the place so im just throwing this out there as I believe Ken was thinking the same thing as I.

Driver is up to date...
The only thing left is the motherboard, processor , and ram. 
 
Ok...I now have to devise a different method.  I will record all the midi tracks as audio.  Then delete the midi tracks.
 

Converting those 7 external synth midi files to audio, then deleting the midi files from the project may have worked.  I stopped the project, forwarded it to the end of the loop region and pressed play and the curser returned to the beginning and the song played.
 
Perhaps a midi round trip from sonar to an external synth takes longer than an audio round trip, and there are all kinds of variables that can affect the time it takes:  buffering and latency in sonar, buffering and latency in the external keyboard, latency in the midi UM-3G, midi cable length...who knows.  Man I hope this song keeps playing...

That was it.  Midi was causing the screen freezes.  To be specific in this case, externally routed midi to and from an external hardware synth (MOX6).
 
I now have two versions of this project.  One all midi files and one all audio files.
The one with midi files crashes Sonar.
The one with audio files won't crash no matter what I do to it...even machine-gunning the spacebar.
 
So, Sonar.  Cakewalk.  What is the problem.  Midi?  Me?  You?  Microsoft?  Or Yamaha?
 
I have been here since Pro Audio 8, and the old Cakewalk Newsgroup.
My old name was R*lpo Mirac*lous, r*chiedoc, R*ch** M*ll*r, so some of you may remember me.
I wish I had my old forum account back...I lost control of it somehow...now I'm just some newbie with issues.
And I just bought the lifetime Updates pack.
 
Hello to all my old friends here.  Thanks for all the ideas over the last 6 weeks on various threads.  Good luck on your projects.  Relpo out.
 

Hi, Relpo. Sorry if this is obvious, but is everything up to date? MIDI interface (http://www.roland.com/support/by_product/um-3g/updates_drivers/350805 ), AI drivers (https://www.music-group.com/Categories/Behringer/Mixers/Analog-Mixers/UFX1604/p/P0AB3/downloads ), Windows etc? 
Have you tried different driver modes, compatibility mode etc? 
All the best.