Problem...
I appear to have lost my entire database, and I do not know what I did to cause the, but I see that I do have the sprite file, and it is unchanged. How to I regain access to the database? I hope that I am explaining this correctly.
First, make a copy of the entire folder containing zotero.sqlite and place it somewhere as back-up.
You've tried restarting Zotero?
When you show your data directory from the Zotero preference --> Advanced --> Files and Folders, is that the folder containing your zotero.sqlite?
Have you tried just restarting Zotero?
I think that I may have lost as many as 250 entries. Fortunately, I have an older copy on a different computer. But that is little comfort at the moment.
By way of a simple question: why isn't the program separated form the data, or am I wrong about that? At least, the programme appears not to be separated form the data. Again, thanks for your effort to help. I still have the file zotero.sqlite from before the event, but I do not know what to do with it at the moment since it is being rejected.
There's not really any way to just lose items in Zotero. It's possible 1) some items haven't yet synced from another computer, 2) you accidentally deleted items (say by using "Delete Collection and Items…" on a collection instead of "Delete Collection…", 3) Zotero somehow ended up pointing to a different, older data directory on your computer, or 4) you have your database in a cloud storage folder like Dropbox and your database was corrupted.
The way to restore from a database file is
https://www.zotero.org/support/zotero_data#restoring_your_zotero_library_from_a_backup1
so try that with the backed-up zotero.sqlite