It's Win10 Home (or whatever the latest standard non-pro version is called these days.)
It was an update from Win 7.
I have four partitions. C: with Windows, a Data partition, a backups partition and a software partition. But CCleaner was installed to C:
I use Avira AV software. Free Version.
Though I do not dual boot the OS in the normal way of things I do have Macrium Reflect set as an alternative boot mode if I need to boot to a recovery image. I assume that this uses the boot loader in the same way as dual booting would.
It did seem as if Ccleaner has been removing a file that Windows boot loader wanted to see. Because it crashed right at the start, before the screen with the Windows and Macrium options appeared.
I haven't made any changes to Ccleaner's settings.
Before each of the crashes I had only used it to clean up temp files etc. each time. Not for registry cleaning or start-up control.
It did have a lot of log files in the clean list, from Office 2010. I'd not seen that with previous Ccleaner versions as far as I can recall.
It's been working fine in previous versions, since Win 10 first came out as an update. (And previously)
(BTW very useful for ditching the "apps" that Win 10 foists on users. I've been recommending it in forums for that reason).