Failure to boot - No Media Present

Hi, I have a 3yr old PC from yourselves. Been absolutely trouble-free, but yesterday failed to boot, and on trying to start up, it does a "Checking Media Presence" to which it comes up with "No Media Present" result.
The PC has a 1TB SSD installed.
That morning some of my open windows had closed, so I think there may have been an auto-update/restart overnight.
On starting, It offers some options for Windows auto repair, but nothing I've tried has changed anything:
In command line, I used Diskpart to list disk, and it showed just the headings but no entry. Tried 'rescan' and it found nothing.
I can get into the BIOS, and saw that the Boot order didn't have the "Windows Boot Manager (1TB SSD)" as the top option, so I changed that. Same result, although the screen is now a better resolution in the windows repair mode.
I tried uninstalling the latest update, and I think it did that. It starting doing something and then the PC restarted, but still with the same failures.
I can get into the BIOS so I can see lots of interesting stuff I don't understand, but nothing as straightforward as showing me a failed bit of hardware...