The fastest solution may well be to reinstall Yosemite. You may not be able to definitively diagnose the problem, but reinstalling will probably take a shorter time than troubleshooting.


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