I'm pleased to say that copying an older version of the normal.dot template file from the laptop solved the problem. Even when I thought that might be the answer, it did take a while to find the right template folder, which is well buried in the folder structure, but I did find it and the replacement file did the trick.
*Sigh* I get really wound up when things don't work. I know I shouldn't; my emotional state was out of all proportion to the problem. I could have used Open Office. I could have used the laptop (which I did actually begin to do, only then I had the brainwave about the normal.dot file). I still seem to be suffering from residual stress from all the overdue deadlines (only one more assignment to go now!) and I desperately wanted to finish critiquing the stories my students had posted for the first tutorial, so there was a Last Straw quality to the total collapse of Word.
Anyway, I'm ploughing through the critiquing now. Onwards and upwards!