In th end I forced it off by holding the power button down and restarted. A brief flash of the Acer screen, and then:
Check cable connection!I have put the above message into Google (after resurrecting the old Lidl cheapie laptop) and it looks like the hard drive is toast. The less alarming alternative is that it has somehow been reconfigured to boot from a network, which it never has done and is not set up for, and that all that is wrong is a changed setting. But I have checked in the BIOS and reset to factory settings, and it doesn't help. The BIOS does not give the option of disabling the network boot, just moving it down in priority. And who changed the setting anyway? I was eating scrambled egg at the time.
PXE-E63: Error while initialising the NIC
PXE-M0F: Exiting Intel PXE ROM
No bootable device - insert boot disk and press any key
Last time backed it up was ... er ... November?
This is going to be awkward. All my money files, and six months' worth of photographs, and all my Outlook emails and calendar stuff, gone.
If anyone reading this has the faintest notion of clue, will it be possible to take the HDD out of the netbook and plug it into another computer so that I can at least recover the lost files, even f I can't boot from it?
In the words of Captain Darling:
The Lidl cheapie laptop is also showing signs of extreme unreliability (why I got a new one, as I recall), so if I seem to disappear from the face of the Interwebs, I'm probably just involuntarily incommunicado, at least until the shops open.