I had done a complete uninstall of CCleaner v512 using Revo Uninstaller in case there was malware clinging to any of the registry keys associated with CCleaner. I did that in SafeMode and downloaded the latest version of CCleaner which was version 514, installed it and ran it in SafeMode. Then I rebooted the computer and ran CCleaner again (Analyze and Run Cleaner) and this time, it did not shut down my computer. So...it would appear that the issue is resolved.
However, there was an issue with version 512 shutting down my PC and like I said, I could not find anything to indicate there is any malware aboard my system. I run all of the best recommended diagnostic software for malware out there to make sure that I don't miss some of the most difficult to trace spyware, malware and viruses, including PUPs, rookit infections etc. particularly since Microsoft doesn't support XP anymore.
Have any other XP users had this issue? I noticed one user in a pinned post with SP2 had an issue similar with version 509, but theirs was restarting their computer, not just shutting down. My issue was happening for weeks. CCleaner had been shutting my computer down and I could not identify why it was shutting it down or what was the cause of it shutting down by itself until today. I thought you should know. Cheers!