Screen turning off too soon

Hi.

Every time I leave my laptop working, (updating, recording something, downloading etc) The screen reverts to the lock screen image after a few minutes, requiring my pin to open. During this time the process has stopped, restarting when I sign in. 

I have checked the various timeout settings and they're all set to 'Never'. I have reset them to default, restarted the laptop, and reset them to 'Never' again. No change.

I've checked the screensaver, which I never use, and it's set to 'None'. I enabled a screensaver and set the timer to an hour. No difference so I turned it off again.

I checked for a proximity sensor but this xps13 7390 does not seem to have one.

I finally factory reset the flipping thing.....AND...it's still the same.

I want to be able to leave it running doing some job with the screen live until I turn it off.

Any suggestions, please. 

Ps. Words of one syllable please. I am Very Old.