Checked Event Viewer this morning and saw this message:

"Cleaning up corrupt content index metadata on c:\system volume information\catalog.wci. Index will be automatically restored by refiltering all documents."

Could Windows be repairing itself? (I did disable the faulty floppy controller (for 3-1/2 inch disks) in Device Manager, Properties.) Things do seem to be a lot more stable now.

Yes it is repairing itself. No action needed. It's to do with Windows searches and the Indexing Service, which speeds up searches. Some people disable the Indexing Service to speed up the computer rather than have faster searches. If the error keeps arising, it can be caused by various other errors. Crashes or bad shutdowns maybe.