Today I tried to run Platinum and instead of running, SOnar begins to start and then an installation pop-up appears. This pop up doesn't say what's installing and it never closes. If I manually hit cancel it just sits there saying it's closing, but it never does. 
 
Does this mean my Platinum days are over?

Sonar Platinum works fine for me.
 
Are you sure this isn't a plugin's dialog that has popped up as part of the VST Scan?

I'd say that Platinum days are not over.
 
It's scanning my plugs as I write. And the start screen is there. 
 
However it may take a while to fully confirm because I recently installed Waves Mercury V10 and ha d not opened Platinum since then.
 
I'll report back later.

It's working here on win8.1 as well as CbB...

It sounds suspiciously like adware.... double check with both adware protection and anti-virus...

Works for me.
 
Do you have a steinberg / yamaha ur22 or similar audio card? If yes, and a Windows installer popup appears, you simply need to reinstall the drivers.
 
Anyway, I am satisfied with Cakewalk Bandlab….. (so, in my opinion, there's no need to use "previous versions").
 
Regards,
 
Giorgio

There may be an unseen prompt behind the main window, waiting for you to click an "OK" button you can't see. Try pressing the Enter key when it appears to be hung.
 
The good news is that no, it's not SONAR breaking.

joegab
Do you have a steinberg / yamaha ur22 or similar audio card? If yes, and a Windows installer popup appears, you simply need to reinstall the drivers.

Likely what is reported here (if the OP .sig is accurate the UR44 may the the cause in this case). It has been reported here before and on other forums. Affects several audio related programs.

Had the same problems using an Ur22 mk on my laptop,
got rif of it by installing :
Yamaha Steinberg USB Driver 1.10.1 · 6 MB
 
 
If this doesn´t help read this article from Steinberg ::
Windows 10 - TOOLS for UR: 'Preparing to install'Problem
After a major Windows 10 update, the TOOLS for UR software does not work correctly anymore. Opening the dspMixFx application or starting Cubase/Nuendo initializes a Windows Installer dialog stating 'Preparing to install'. The Windows Installer has to be closed using the Windows Task Manager ('end task').
Solution/Workaround

• Uninstall TOOLS for UR and the Yamaha Steinberg USB Driver completely.
  (Right-click on Windows logo at the bottom left > Apps and Features)
• Restart the computer.
• Install the latest Yamaha Steinberg USB Driver.
• Install the latest TOOLS for UR for your interface (UR44, UR242, UR28M, UR824).

The error message should not appear anymore and it should be possible to access 'dspMixFx' and load Cubase/Nuendo normally again. 

 

Thanks everyone. It did turn out to be the UR44 driver. Strangely it was still working fine in Reaper and Mixcraft so I never would have figured it out on my own.