Still XP. Thanks for tolerating.
I cleaned up my mess.
Last week, I started making trouble by changing the account name in Control Panel > User Names. It was annoying to see the account's top folder in Documents and Settings didn't change.
I had to go into Safe Mode to force Windows to allow me to change the top folder name. (I shouldn't have done that.)
When I was done forcing my will, the top folder for the account with all the old data had a new name.
But somehow, Windows created an additional top-folder in Documents and Settings with the old, original account name. It was empty, except for some new-account default files, mostly for Windows Media Player and Bill Gates advertisements.
I thought that Opera was crazy, getting its user data from the empty account, just because it had the original account name. It was keeping me from accessing my million bookmarks.
But then I did a right-click on the Windows button, selected Explore, and found that Windows was also going into the empty account folders by default. Instead of looking at the desired folders with all the good, old data, Windows was looking at the empty folders, apparently because their top-folder had the old account name. Windows was refusing to change its default of going to that old account name, even if it had to create a new account-folder with that name. Sorry about the red herring I gave leocg, when I said Windows was back to normal.
And I guess that's why Opera was looking at the empty folders, too.
This is how I cleaned it up. I went back into Safe Mode. I deleted the mostly-empty account. And the 30 GB top-folder with all my data that I had earlier renamed, I renamed it back to the old name -- the one that Windows keeps looking for by default. That pretty much put everything back the way it was originally.
That worked. Windows and Opera are looking at the correct folders for the good, old data. I have my bookmarks, etc., back. I also have my old desktop back.
I need an aspirin and a defrag.
Meanwhile, in Control Panel > User Accounts, the account name is still "changed." So, that's all that changing the account name there is good for -- what's displayed in that User Accounts window, and maybe for logging in and out, which I never do. But it doesn't change the name of the top folder for the account in Windows Explorer > Documents and Settings.
Regarding g00g00's link for re-directing where Opera looks for "user-data," it didn't work for me. They give examples of paths for Chrome and Chromium, but apparently Opera uses different folder names so I wasn't able to apply their instructions, either directly or by inference comparing to the folders I was seeing in This Old Computer. For instance, the path includes a sub-folder named "User Data" which I couldn't find in any Opera folder or subfolder. But the author of the article uses shorthand for folder names, which eliminates preciseness, so maybe the folder "User Data" is actually named something else. If so, don't ask me what. I couldn't find anything close.
I started googling for "Opera User Data" for paths special for Opera, but that's when it dawned on me how to undo my mess.
If the instructions had worked, I might not have struggled to put the computer back the way it was originally. I think this is best.
I don't use the Account functions very often. If I feel the need to change something next time, I'll google for instructions instead of making up my own.
Your suggestions got me working in the right direction, so thank you both.