Well, 8 1/12 hours trying to fix this today is enough.  Interesting followup:  Not only does the detested X1 work, but so do Home Studio 7, 6, 4 and Sonar LE, and Sonar 8! (pre 8.5 update)--ALL still on my machine, and ALL still working. It's "only" 8.5 that's broken now - the only program I've used for years.
 
Somewhere there's a logical explanation, somewhere there's a fix - But this is really one of the worst experiences I've ever had on a computer.  Working away happily - try an upgrade demo-- DESTRUCTION in its path.  And in a particularly wicked way, whatever the frick happened didn't phase ANY other Sonars I have on the computer - just the one I love and use.
 
It doesn't matter to me that we can slough the problem off on Windows -this is totally unacceptable sh!t.  SOMEthing is going on with that Sonar X3 demo that played havoc with my home studio, and if I could sue someone- I'd be on the phone to a lawyer NOW.  I'm devastated.
 
I'll open my curtain project in one of the Home Studios to limp along finishing it.  Talk about a BIG step backwards--good god- haven't seen those programs in many years.  At least they open and the current project plays.
 
Randy

Sorry this looks like a Windows issue which was trigged by Sonar.
Your lawyer would have told you to back up your system first, please get yourself a 4tb external USB hard drive and a copy of Acronis True Image before you install any software next time (sorry not what you want to hear now but in future this may be good advice).
 
Anyways have you tried the 32 bit versions of the C++ libraries?
 
You say 8.5 is broken, 32 bit, 64 bit or both?
What is the error in the Windows event viewer?
Please can you explain what is happening in full detail.
 
(Oh and another thing, you could try a Windows recovery point). 

CakeAlexS...Your lawyer would have told you to back up your system first, please get yourself a 4tb external USB hard drive and a copy of Acronis True Image before you install any software next time (sorry not what you want to hear now but in future this may be good advice).
 
Anyways have you tried the 32 bit versions of the C++ libraries?
 
You say 8.5 is broken, 32 bit, 64 bit or both?
What is the error in the Windows event viewer?
Please can you explain what is happening in full detail.
(Oh and another thing, you could try a Windows recovery point)

After 8 hours of trying to fix this earlier, I took a chill pill to at least escape with sleep.  Back at machine - AND I need to give you a bunch of Gold Stars, Alex, for trying to help out. - Taking your items in order:

--I didn't save a system image.  I do have quite a few, but frankly they go back way too far.  Didn't occur to me to worry about doing one with such a mundane everyday thing as trying another Sonar demo.  Yep, should have, but I wouldn't have anticipated a problem in a million years.
 
Yes, I've tried both 32 and 64 bit C++ files - have them all, have run them all.

Both 32 and 64 bit versions of Sonar 8.5 no longer work.

NOTE:  Every danged single other version I have of Sonar on this machine works.  It looks like I'm going to try to finish my current project in Sonar LE, of all things.

In Windows Event Viewer clicking the big red Error exclamation point under applications:

Faulting application name: SONARSTD.EXE, version: 17.5.0.141, time stamp: 0x4a9774b3
Faulting module name: MSVCR90.dll, version: 9.0.30729.6161, time stamp: 0x4dace4e7
Exception code: 0x40000015

Tried Recuva since info on line says that .dll must have been deleted BY A RECENT INSTALLATION.  Recuva seemed squirrely, kept locking up, using its search didn't find MSVCR90.dll.

What is happening is I try to open either 32 or 64 bit Sonar 8.5, and there's the error message:

Microsoft Visual C++ Runtime Library Runtime Error

Program: C: etc

This application has requested the Runtime to termininate in an unusual way.
Please contact the application's support team for more information.

I have tried Windows Restore twice today, after waiting a long time, both failed.  First time that's happened.

Confirming again that ALL versions of Sonar on this machine work, except the only one I want to use - 8.5.  That's all 8 of the other Cakewalk/Sonars, the Home Studios, X1 both 32 and 64 bit.

I'll try to refrain from hyperbole--BUT - this, for me, is nothing short of devastating.  My program's dead.  Thank you so much, Sonar fricking X3 demo which never worked.  And natch, goodbye to the things I was hoping to get today in Sonar X3 Producer that I was robbing the piggy bank to buy!

Randy

Randy your scaring the hell out of me as I just paid for the upgrade to X3 Studio!
 
But a few things that I'm thinking. 
 
First, this sounds to me like your downloads are not complete, Like there is missing data. And your saying both X3 and you re downloaded 8.5. Do you not have a copy of 8.5 stored to a disk or Hard drive? I myself am always reluctant to buy software via a download for this very reason.
For my purchase I am going to go to a location where I know the internet is stable and will not cut out. At my house this is not the case. I also have been at a few other locations where the internet cuts out for a few seconds. 
 
Another small possibility is something did go haywire with your computer and it is just a coincidence it happened at this time.  
I don't know if you have this option, but I would try to install on a second computer just to test this theory.
What I might do is install my X3 on a fresh C drive. This way I'll still have my original set up easily restored. Hard drives are cheap and a C drive doesn't need to be very big. All my data is on other drives so it's only the OS and software involved. Sure it's a PITA but I'm into 3 years with this drive so it is on my list of housekeeping duties any how.  I hate this kind of stuff.  

Cactus Music...First, this sounds to me like your downloads are not complete, Like there is missing data. And your saying both X3 and you re downloaded 8.5. Do you not have a copy of 8.5 stored to a disk...
...Another small possibility is something did go haywire with your computer and it is just a coincidence it happened at this time... 
...I don't know if you have this option, but I would try to install on a second computer just to test this theory...

Thanks for the reply Cactus.  Yes, I also made a hard copy of 8.5 along with the update patches.  After reading your post, I reinstalled once again, this time from the disc.  Same result.
 
The possibility of something happening on the computer simultaneously at exactly the same time as installing the X3 demo is so astronomical - All I did was download the demo, run it - it never worked.  I uninstalled it.  In the wake of it, 8.5 was broken.  It's virtually impossible for the two events not to be related.
 
When I ran the Event Viewer and saw that the "faulting module" was MSVCR90.dll, I looked for that on the computer and found it's only in one program - the Calibre ebook program.  So, I uninstalled that, downloaded it again, installed that.  No change.
 
Guess I've already used the word "devastated" - but that's still the best word.  8.5 has been my program for years.  I love it.  I DETEST X1 - who doesn't?  But I guess I'm stuck with that now.  Sonar LE works, but is of course a toy program.  Home Studio 6 is more equipped, everyone also knows that HS 7 was a joke - I have that but wouldn't consider using it.  Have no idea what's going to happen with old projects and unfinished projects.
 
After spending 10 1/2 hours now trying to fix this, it will really seem like a miracle if some solution arises.  The worst, most traumatic experience I've ever had with software.  It's like waking up to find your car inexplicably not working and you don't have insurance to fix it.
 
Randy

Seeing that the installation is accessing C++ 2005, I went to Microsoft and installed that again.  Yet again uninstalled 8.5, ran from old disc installers, ran the updates - same result.
 
Ever want to just turn the clock back and want to take something back?  Natch I wish I would never have installed that X3 demo - and on a computer, we're supposed to have a way to dial the clock back, with System Restore.  But that's mysteriously broken too - After running it - the report is the system restore fails.
 
It would be extremely hard to convince me that there was something squirrely in my download of the X3 demo.  It never worked, had its own error messages, was uninstalled.  I repeat myself - I'm just sitting here in a daze, finding it really impossible to accept that suddenly my Go To Program is gone.

I see from a search that there were posts about this exact same C++ error after people installed X1.  Curious- Same thing with 8.5 no longer working.  When I installed X1 back when it was released, I didn't have that problem.  Now, here in 2014 I have the same problem they were describing with X3 - the demo at least.
 
AND this is curious-- I've noticed the last few hours, that the MIDI Activity icon, you know in the "Show Hidden Icons" notifications at the lower right?  It's constantly on - I have no MIDI device turned on, but it's constantly on.  Before this, it only showed up when I turned my keyboard on or opened Sonar.  Task Manager reveals nothing MIDI related still running --- Have to wonder if it's related.
 
Randy

Isn't the X3 Demo brand new? 
In the past we have always said that yes you can SAFELY install a new version of Sonar alongside of other versions. They apparently don't acknowledge each others existence but for the Plug in sharing. Didn't you say you had Sonar 7, Wouldn't that be the closest version? Wouldn't it use all your newer plug ins?
 
Another course of action would be to start fresh and re install your OS. I would almost guarantee that all would work again. After all, it's not like your install disk has changed. It is obviously a virus like symptom caused by the X3 demo.
I re do my OS as a matter of course to keep my hard dives new every 3 or 4 years. Sure it takes a few hours but works wonders for housekeeping. Certainly quicker than what's happening to you right now.
Anyhow, good luck I sure hope this resolves itself as I agree that 8.5 was the best so far.
I'm only grabbing the X3 studio version because for $99 it's got to be worth my time to learn the new system before 8.5 no longer runs at all. And like you, Melodyne intrigues me.     

Cactus Music...Didn't you say you had Sonar 7...
 ...Another course of action would be to start fresh and re install your OS...

 
I've tried yet more since I wrote - all to no avail.  Even had a BSOD after the last time I tried to run restore point again.

No, I don't have Sonar 7, I have Home Studio 7 which is an acknowledged Piece O ****e - I'll either try to using Sonar 8 -  omg--before all the 8.5 improvements, or HS 6, or Sonar LE-- I don't know.  None of it is appealing - not after 14 hours now of trying to undo the damage.

Fresh install of the OS?!?!  Are you kidding - Last time I did that it took me a full two weeks, 8 hours a day reinstalling everything, setting things up and yadda-- Right now I REFUSE to do that just because of a fricked up demo installer.

So disgusted.

Randy

Hmm, takes me about 3 hours, OS, Sonar, drivers, Win amp, Wave lab, done. Oh, copy plugs to vst folder.