On Thursday, 24 January 2019 08:59:01 UTC, Iain wrote:
Left my computer switched on when I went to watch a bit of TV. About an
hour later I heard sounds coming from my office and went to investigate.
The computer was playing the last utube video I had been watching. I
powered the computer down and went to bed.
When I switched the computer on this morning the damned thing started
playing the same video again and at this point I had not logged on!
anyone got any idea as to what's going on?

Iain

I suspect that whilst you felt that you had powered it down, it had actually gone to sleep. I keep finding people who think they restart their computers every night, or at least regularly, yet the last reboot date is weeks or months ago.

In Power Options you will likely find that using power button is set to send it to sleep. This applies both to the physical power button AND the on-screen power-off.