DickVerbo

Thanks, safe mode worked! As for the flat new version ... I'll reserve judgement.

I forgot to say, after the failed Uninstall, JV16 Powertools no longer detects CCleaner as software, so I can't try the 'Force with reboot' option.

I'm now in a worse place than I was when I started. I downloaded JV16 Powertools, and tried 'Uninstall' rather than 'Force Uninstall with reboot.' It deleted the desktop icon, the Languages folder and unist.exe, but left CCleaner64.exe. Installing CCleaner v5.0 still hangs in the same place. I've made a Desktop shortcut to still use the old version. Hopefully that's okay. Question: Won't uninstalling CCleaner remove all my settings, plus my include and exclude lists?

Same for my Win7 64 bit PC. Installing hangs immediately after it begins, at roughly 3% of the length of the green progress bar. Unfortunately, clicking on 'Details' just gives me a blank box with no text. I've tried running uninstall first (uninst.exe, 150KB) but that hangs as well (at about 30% of the progress bar.) I'm trying to update from V4.19.4867, which still works perfectly well. This is the first problem I've ever had with CCleaner, and I've never had to uninstall between versions before.