Thanx for trying to help, I'm at my wit's end. Have recently installed other software--no issues. The link you provided doesn't speak directly to PS, but it is an insufficient disk space error for Creative Suite. If that were the case, we have about 25GB available (on D drive where we need to install it).
System Restore is not an option as I mentioned in my original post. I have only 6GB on my C drive (all of these companies think their stuff is hotter than everyone elses and will direct their software to install on C regardless of where you specify--even those that permit it in a custom install--and even when C is set as the default drive in the registry) and of the only 2 restore points available, one did not work and the other was the same day's restore point, which after restoring, did not correct the issue.