At this point, it may be best to bite the bullet and reinstall the entire OS from the DVD. Sometimes, the nuclear approach is faster and easier than trying to troubleshoot. At least, that's what I would do.
Jon
macOS 11.7.10, iMac Retina 5K 27-inch, late 2014, 3.5 GHz Intel Core i5, 1 TB fusion drive, 16 GB RAM, Epson SureColor P600, Photoshop CC, Lightroom CC, MS Office 365
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