DB access error on two OLD 2.3 sites after installing 2.3.1 on NEW site

This one’s a mystery beyond me. I do have one clue that might be key.

(I’m self-installed on a hosted PowWeb server using MySQL 5.0.45, PHP 5.)

The background:

I had Site 1 and Site 2 (both 2.3) installed in subdirectories. They worked fine.

Today I bought a new domain, created a subdirectory folder for it (call it Site 3), and did the “5 minute install” of 2.3.1 (note: again, Sites 1 and 2 are 2.3, not 2.3.1).

Now Site 3 works, BUT: Sites 1 and 2 get an “Error establishing database connection” message. I can’t get into them.

POSSIBLE CAUSE:

I accidentally FTP’d the unzipped 2.3.1 WP files into the root directory instead of the Site 3 subfolder. So I went to the file manager and moved all the files from root/ to root/site3.

Then the install for Site 3 worked fine. Still does. But 1 and 2, which I hadn’t touched during this process? They’re inaccessible.

Any ideas?