Sound update:

I connected last night to the TV, and sound worked OK, but after restarting laptop today, onboard sound has been knocked out again! Back to Dummy Output. I see this on the sound settngs, but no onboard sound:

and this is what I see on pavucontrol:

The drop-down list on the last tab looks bizarre. Obviously I realise that whack-a-mole is not much of a method, but I've tried all of the options, and none of them produce sound:

PS, sorry if I've put this on the wrong forum - please feel free to move somewhere more appropriate.

And PPS, it's Ubuntu 16.04.6 LTS,  to be precise.

Right, it looks like no-one is ever going to reply to this thread. I'll go and post elsewhere for whatever the remaining issues are. I'll just say (in case someone comes on here looking for answers to the last two of my questions) that the shutdown issue was in fact a software thing. It was due to the fact that I have Cairo Dock installed, and had it opening at system startup, which for some reason was knocking out the shutdown option. Strange one. As for the Super key thing, I have no idea why that was (or rather wasn't) happening, but I was able to resolve that by assigning Super as a keyboard shortcut with the following command: dconf write /org/compiz/profiles/unity/plugins/unityshell/show-launcher "'Enabled'" Thankfully those were not Dell issues, but I do fear that the first two are, and that is why it's disappointing not to hear anything back here. But like I said, hey ho, I'll try somewhere else