Still struggling with this "panic" issue, I browsed Apple's website this afternoon, and came across a Contact page (
https://getsupport.apple.com/) which surprised me because it simply asked for my phone number (and Apple ID, of course), and a few minutes later (really), the phone rang, and sure enough, it was an Apple technician. He directed me in running several procedures and tests which led him to conclude that the problem was in Apple's software (the OS) and not the laptop's hardware or apps. I never got the feeling that he was in a hurry, or that he had two or three other callers in his ear at the same time. Eventually, he suggested I reinstall the OS. He told me precisely how to do it (although it was clear he would have walked me through it if I had asked him to do so). Anyway, that's what I did: not a clean sweep of the disk; just the OS. He seems to have been right because Apple>>Start and Apple>>Restart now work properly and Photoshop opens graphics properly. I will continue testing apps for a while just to be sure, but so far so good.
The question of payment never arose. Nothing about the expired warranty (my laptop is six years old), nothing about my purchasing an "extended warranty." It was a free call and free service. I suppose if more had been required, eventually money would have changed hands, but not today.
I have to say I am stunned. It reminded me of the old days, the original days, with Dell. I had occasion to purchase several of the very early Dell desktops, and they came with a phone number ... which was always answered by a helpful technician.
As I wrote in an earlier entry, I really like this Mac laptop. This evening, I like it even more. Any potential switcher out there, consider the word of this long, long time Microsoft user: This is not only a great product, but my experience today indicates it is backed up by real support.
Thank you to chscag, pm-r, and others who showed an interest and offered help. I appreciate it. This is the first Mac-related forum I joined after purchasing the MBP, and I am grateful for it.