Are you cold booting or coming in and out of hibernation? When you power back on do you see a text startup screen and then it goes dark with lots of disk activity?

Hold the power button for >10 to do a full shutdown and reboot. If that doesn't do it unplug the charger, pull the battery for a few seconds and then reinsert it. That will do a cold start of the PC

It could be in the middle of today's update. As Hoople says, you may need to do a full restart, and, possibly, run the updates again.

Ok, I went to the pub and had a couple of beers, came back and it sort of switched on. It was very jittery and the login box jumped all over the place however after about 10 minutes I was able to enter my PIN. I left it for a few minutes, switched off, left it again and then it switched back on again.

This morning it's switched back on totally normally and says it is downloading updates therefore I'm just going to leave it alone and see what happens ... what an awful user experience plus I'd bought this thing for travelling with, now I don't know whether I can trust it!

I'll probably have a look round for another small machine and put Win 7 or Mint on it.

Probably worth running one of the anti-virus scans, or online spyware scanner. It won't do any harm.

It's completed an update, I'll run Malwarebytes however I've a feeling it's the very poor update installation since I've just spoken with a friend and he's just experienced precisely the same, interestingly on a very expensive Lenovo laptop.

It's also a sign of a failing hard drive. Run an error check (requires reboot) and see if it fixes anything. MAY require a few passes to get it all.

Then look at the hard drive's properties for SMART (health) info - OK, some errors, pre-failure warning, etc.