Down loaded the free regular version, and it starts install normally, but pro version just opens a window with a blue screen background. I downloaded on multiple occasions - same result.
That sounds very odd. Lets see if we can work out what is going on.
Do you mean that the installer is bluescreening, or that the installed CCleaner is bluescreening?
Could you post a screenshot of what you are seeing?
(I have authorised you for posting images).
Where are you downloading the Pro version from?
Do you already have a Licence key to activate CCleaner as Pro, or is it a trial that you are trying to download?
A few more general questions that may also help:
What Windows version are you running?
Do you have any Themes or Accessibility options set?
Are you running an AV other than Windows Defender?
Are you using a VPN?