The apparent order of events was as follows:
1. I noticed that the active monitor profile on 14 Dec 2017 was not my most recent. Moreover i1profiler couldn’t see my monitor. When I tried to re-profile the monitor, the calibration software, i1profiler, wouldn’t work.
2. I was advised to update my graphics processor. With help from NVIDIA I did this.
3. Then I re-profiled the monitor and edited a file in Lightroom, apparently successfully (16 Dec).
4. When I finished I turned Power to Sleep. But the computer tried to turn itself back on but not very successfully. The Dell logo came up and the circling ring of circles, but it got no further than that (all night).
5. With difficulty, I rebooted the computer. Finally it informed me that it was corrupted and needed to go back to an earlier point. It did that and restarted. The correct monitor profile was still showing.
6. I clicked on Lr Classic CC 7.1. And it instantly crashed and told me that my catalog was corrupted and, ignoring all my recent backups, gave me the option of opening two very old catalogs which would have lost me 2-12 months of work. My most recent backup dates 13 Dec 2017.
7. When I tried to open a more recent catalog, Lr opened but it couldn’t see the catalog. I got an error message: ‘assertion failed’. Lr invited me to send them a crash report which I did (23 Dec, I think). I have had no response so far.
8. I suspect that all of this happened after I updated to Lr Classic CC 7.1. But there were also Windows and Dell updates around the same time.
9. What can I do now? Should I reinstall Lr? I have never before needed to do that. Are there any recent instructions about how to do it.
Dell XPS 9700, Processor: Intel® CoreTM i7-4790 CPU @3.60GHz 3.60 GHz; Installed RAM 16.0 GB; 64-bit operating system, x64-based processor; Windows 10 64-bit; Version: 10 or greater 10.0.16299.15. NVIDIA GeForce GTX 745 / Version= 126.96.36.19959. Adobe Photoshop Version: 19.0 20171103.r.190 2017/11/03: 1143799 x64. Adobe Photoshop Lightroom Classic CC; ver 188.8.131.52