OK thanks for all the advice. Have now unplugged the PC as a new one has arrived. This was going to happen this month before all this windows mess. I shall rig the old one up in the spare room and come back to this thread. In the meantime - working out how to connect a monitor to this new PC - O joy.
You should have double the fun now! Your new PC will probably have
a. trialware on it (to uninstall)
b. Windows 10 1803 - so at some point it will seek to upgrade to 1809.
Your earliest priority should be to start using disk imaging routinely before making significant changes.
Image Windows with e.g. Macrium Reflect (free) - you need a large enough external disk or similar, preferably USB3.
Then as you make changes, keep a simple log, and at appropriate intervals create a differential image.
You may wish to consider whether you want Windows update to run at all at present.
1803 has bugs with default associations; latest (informally) on 1809 is that many of the known bugs as still not fixed.
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