You say that you sometimes run a dual display set-up. Could there be a window currently off-screen waiting for input that seemingly makes Sonar freeze? Perhaps somehow being placed there during a different monitor set-up?
 
And also, does this happen regardless what template you use to create your new projects?

Canopus
You say that you sometimes run a dual display set-up. Could there be a window currently off-screen waiting for input that seemingly makes Sonar freeze? Perhaps somehow being placed there during a different monitor set-up?
 
And also, does this happen regardless what template you use to create your new projects?

Well, i have tried both undocked and docked in both dual screen and single set-ups. That was my first thought as well. But no. The single screen setup is giving me the same problems with everything dock (or undocked, for that matter).
 
Also, the same empty template saved as a normal project file is giving me problems (so, no plugins, no data, no wavs, etc..). When i then (after the failed loading) reopen the same template, everything is working (within that template) as it should. The problem appears when i try to open "a" normal project file and only then. Ow,,i've tried the bundled filetype as well, without succes.
 
And yes, all templates (and then saved to a project file) aren't opening the way they should.

Just a shot in the dark – have you tried to simply press Enter once or twice when things lock up? So if there after all is a hidden window somewhere waiting for input, and the dialog contains a default button, things might get solved? Or optionally the Escape button?

Canopus
Just a shot in the dark – have you tried to simply press Enter once or twice when things lock up? So if there after all is a hidden window somewhere waiting for input, and the dialog contains a default button, things might get solved? Or optionally the Escape button?

Yeah. I also looked inside task manager to see if something else is running "beneath" SONAR. But, no. No luck...My guess is that the mixer is giving me problems. That screen is acting up (docked, undocked, whatever).

Another shot in the dark:
Unplug your audio interface and open the projects (ignore warnings of no audiocard - and don't save the projects!).
Just to see, if it is not up to your audio interface, worng buffer settings in SONAR, USB-Port, cable ...

THambrecht
Another shot in the dark:
Unplug your audio interface and open the projects (ignore warnings of no audiocard - and don't save the projects!).
Just to see, if it is not up to your audio interface, worng buffer settings in SONAR, USB-Port, cable ...

I can try that ofcourse, but this wouldn't make sense for the properly working templates...

THambrecht's advice is good. There is a big difference between template files and project files and in your case project files are not loading. I would also unplug any midi controllers and control surfaces you have and even every other external component you have connected (not including screen mouse, keyboard obviously) just to see if that could be the issue. I had a problem with a surface that suddenly kept making Splat crash on load.

35mm
THambrecht's advice is good. There is a big difference between template files and project files and in your case project files are not loading. I would also unplug any midi controllers and control surfaces you have and even every other external component you have connected (not including screen mouse, keyboard obviously) just to see if that could be the issue. I had a problem with a surface that suddenly kept making Splat crash on load.

Already tried without midi devices. And now, also without any other device attached. Still, no solution.

hahaha...this is weird.
 
So, i opened the basic template and set that one to be the default one to load at startup. And now, it DOES work.
So, if i set my own INIT template (based on the basic template) as my default, all saved projects won't load properly. But of i set the Basic template as my startup, everything is working....???
 
So i can't use my own (very simple) INIT template as my startup template...
 
So, i undocked the mixer (that's how i want it to be), removed the preview channel and the audio and midi channel, saved that to be basic.cwt, saved it into a project file and...........no luck....it won't open properly. The basic.cwt (original, which i saved as a back up) is still working fine...
 
What is happening here? 
 

And you tried without the audio device connected too? It seems it can only be a problem with your system - software or hardware. It's not Sonar as no one else is having this problem - you have reinstalled Sonar? We can rule out an external device now. Does Sonar actually freeze or just seem to remain busy/loading. If the latter, how long have you left it to load for?
 
Problems like this are very frustrating so you have my deepest sympathy. It could possibly be a registry issue, but that may not be easy to find and fix. I suspect the next step might be to do a clean install of Windows.
 
I hope you manage to resolve the issue and get back to creating again ASAP!