Thanks for the response.
VLC is my favourite too. Because I was trying to keep things to a bare minimum I didn't install it and just used WMP initially. But because it didn't work well, I installed VLC but the results were identical.
The files I tried to play were about 0.12gb, a bit under 0.3gb and under 0.7gb.
Task manager showed group policy client was using anything up to 35%, but it was jumping around so much it was hard to tell. Apparently group policy editor isn't on the 'home' edition. My stepdaughter installed it to enable the necessary change but now there's something called wsappx doing the same thing.
I was trying to see how I could stop that - something to do with MS store - but I couldn't find anything and got tired of looking and took a break.
So, if you reckon it might be that W10 is just too big for the 2gb RAM to cope with and streaming and playback, might scrapping W10 and using something like Linux instead be better?
It would be no loss no longer having W10 as I have it on my main laptop and the spare (both running very well). If I can't get this use out of the mini-dell, there's really no point in keeping it.