I suppose I always thought I would upgrade our two Windows PCs to Windows 10 eventually. The desktop has always worked pretty well, and - partly because it is the hub of our home recording activities - I wasn't in any hurry to mess with it. The laptop was in a bad state and I hoped Windows 10 would give it a fresh-ish start and a new lease of life.
As it turns out, Windows 10 refuses to install on the laptop, despite confirming that it is ready to do so. It seems the installer runs into some glitch in the existing operating system installation and just gives up. So it was that the desktop became my guinea-pig installation machine.
And...after displaying this for slightly too long for my liking (doth it protest too much?):
Windows 10 started up and all seems well.