Hi Marcelo,
I had this happen many times exactly as you describe.
If you are running a multi-core processor, 
try this and see how it works.
When running SONAR: In the Task Manager click the Details tab.
Locate SONAR, it may say SONARPDR.exe.
Right click, choose Select affinity, untick CPU 0
This frees up the main core for Windows as
I believe the other cores are for multitasking.
In a dual processor mobo repeat the same for the other processor.
Sometimes the SONAR glitch will timeout allowing SONAR to restart.
It also helps to restart the computer after a while of work.
When SONAR is running correctly,
the keyboard should work okay with the box ticked in
Edit-Preferences-Midi-Devices and then Midi Track Input.
Of course the SONAR glitch will stop the audio and midi.
You can also try this;
When running SONAR: In the Task Manager click the Details tab.
Locate SONAR, Right click, choose Select Set priority, select
Below normal or Low. This frees up some of the CPU demand.
SONAR meter may indicate ok but Windows and the computer
will still benefit. Any method that frees up resources is good.
If you are running 64 bit SONAR, another thing you can try is
placing the 32 bit VST folders containing their 32 bit dll into the 
x64 Windows Cakewalk VST plugins folder. Windows and SONAR
will use them at that location just fine. Simply Scan VST plugins and voila!
In SONAR an x86 Cakewalk folder is only necessary to run SONAR in 32 bit.
Hope all this helps. I also have a working solution for the Bitbridge issue.
 
Good Luck.
David

Well, I've tried all of the options and none of them seem to work. 
With the cold reboot, it works for a while. But then it happens again and I have to do the cold reboot again
I really don't know what to do...

The next time this happens, look in Task Manager, and see if BitBridge is running.
 
BitBridge will load and facilitate 32-bit plugins running in 64-bit Sonar.  IF there is an issue with one or more of the 32-bit plugins, quite often Sonar can flake out, and often will leave BitBridge running.
 
It should eventually flush, OR you can kill BitBridge in Task Manager, OR you can do a cold boot, OR you can go through the process of figuring out which one or more of the 32-bit plugins is having issues running through BitBridge.
 
Many times, folks will choose to swap out flaky 32-bit plugins for more stable 64-bit equivalent ones.  Other folks will try to use a third-party wrapper, called JBridge, instead of BitBridge, and will see if that makes things run in a more stable fashion.
 
ALL of the above is based upon a determination that 32-bit plugins are the cause of your issues, so the first thing to do is figure out if any 32-bit plugins are present in any project where this behavior is present.
 
Please review your failing project(s), and post back on whether or not 32-bit plugins are present in these projects.  I would also ask you to list which ones you come across, from your review.
 
Thanks, 
 
Bob Bone
 

I have this happen occasionally and a cold reboot is the only remedy. Fortunately it only occurs infrequently and on reproducible functions which I can then try to avoid. Can you reproduce exactly what causes this to happen, and if so, can you avoid it in your workflow? Sometimes it is a particular set of keyboard strokes, or a certain set of instructions to a synth, or effect, that causes this to occur.

Bob Bone:
Thanx for your advice, but I'm running windows 7 32bit, so there is no bitbridge running. If there is one of the plugins I have in my computer that's causing the problem, do I have some way of figuring it out?
I really don't know what causes this. I just turn the computer on, try to open sonar and I won't open. 
I'm having some latency problems with Sonar X3, so eventually I get tired of not being able to fix it. So I switch to Sonar 8. Then sometimes I can open Sonar X3, but most of the time I can't. I have stopped trying to use it because it's pointless. I'm beginning to think this software is a piece of crap

>  I'm beginning to think this software is a piece of crap
 
Funnily enough it works for us, so draw your own conclusions ;)
I don't think we know anything about your hardware, are you able to update your footer like mine?
What antivirus are you running, if you are running more than one you shouldn't. Please try removing all antivirus software and trying again. When you are done then reinstall to see if the behaviour persists.
 
Otherwise
Please run windows update several times
Please update your drivers here: http://forum.cakewalk.com/Driver-Boost-m2928792.aspx
Please make sure your sound interface drivers are up to date.
Run chkdsk on your hard drives.
Rename your AUD.INI
 
However - I would suggest backing up/wiping your windows partition/reinstalling 64 bit windows, but no sure if your specs are up to it.
 
Thanks
 
Alex
 

I would call Tech support on Monday am!
 
Please post your specs as Alex suggested,
 
After a cold start of your system and audio interface, try opening the offending project in Safe mode without any plugins enabled. Reopen your project adding one plugin at a time on each iteration if you are successful in opening SONAR. If this is plugin related, you should be able to pin it down.
 
You mention X3, do you have any of the updates installed for X3 as well?

Safe mode is a good idea as well.
Yes install X3D
 
I would go through my steps and others first before you call tech support, they are only going to go through what we've already written, best to exhaust the possibilities first.

Cheers....

TS is going to make him go through and verify all those steps on the phone anyway. Been there done that. They likely have a script to follow and probably have to say that they went through these steps with the customer to pursue additional troubleshooting from DEV.
 
Doesn't hurt to try what was suggested, but getting TS involved as early as possible will help the bakers keep a finger on the pulse of the users. 

Actually they won't go through all the steps, and that's my point, save time on the phone.
 
The answer to the question is often "Yes I've just done that", and if they insist you do exactly the same again, and you know you've done it... exactly what they say... you pause, make a cup of tea, and then come back and lie.
 
Always best get to your ducks lined up first before you call support (if you can) otherwise it wastes a lot of time (and your phone bill).
 
> will help the bakers keep a finger on the pulse of the users. 
 
They read these forums...
 
Just my opinion....