Just happened again while I was in the middle of a scan, but this time it went straight to the blue screen of death without showing that stupid cheesy message I saw last night.
It powered right back up by itself, and I finished the scan using a spyware doctor subscription I forgot I had from an old computer, and deleted 563 "low risk" infections. So much for windows defender and mcafee
I'm not much of a techie, but I'm not convinced SD is going to catch everything, so I'll follow up with the other suggestions above.
Thanks again.