You asked for more information: all of our computers are using Window 10. For antivirus, we use Norton version 22.20.5.9
I have tried all of your suggestions. First of all, I misspoke when I said that I had two individual computer licenses, The first I have is CCleaner Professional Plus, which is a license for 3 computers. I tried to install this on my husband's computer and it would not run. So I thought I must have been mistaken, and only had a license for one computer. Therefore I bought another license for 1 computer. (Yes, it was the Boxing Day Special.) I have since checked and it truly is for three computers. The extra purchase is okay, as we have two laptops as well which I have not installed onto yet.
I uninstalled Ccleaner and then downloaded it from the link you provided. It seemed to install. It would not run. I clicked on Ccleaner 64 and it would not run from there either.
I booted into Safe Mode. It would not run there either.
Now what?
I appreciate any advice you can offer,
Audra