I did an online search (I began to suspect that maybe the problem was no longer virus related). I found this forum http://www.graphicdesignforum.com/forum/archive/index.php/t-5632.html with this advice:
“There is a preference file for every program that you use. If you throw away the current one for [Photoshop], it will create a new preference file when you restart Photoshop. Sometimes those preference files get corrupt when a program or computer freezes, crashes or sometimes for no reason at all.”
“as soon as Photoshop’s starting to load, hold down shift + ctrl + alt (be quick!), until it asks if you really want to delete the user’s settings.”
It worked. I suspect that the virus caused the problem that had to be resolved by dumping the preference files.