I just wanted to "close the loop" on this discussion and thank once again all those who offered suggestions.
I received a complete set of recovery discs that were FedExed to me overnight from Hewlett-Packard. The process took about four hours, but I'm happy to say the computer now loads HW just fine and the problem is solved (though it's still unclear what caused the problem.
Anyway, Merry Christmas to all, and to all a good night!