Roger,
When I encounter a problem like this, the thing that usually works for me is to
turn the computer off at the source - don't just reboot, turn it off. Rebooting doesn't
usually get rid of those gremlins that get in to machines.
Living here in the high country we have more than our share of this. I read a report
several months ago that cosmic rays (which are more abundant here in Boulder
than in the flat world below) cause about half of the problems with computers. It
seems that they hit some circuit an disrupt the logic. The only way to get back
to normal is to restart the computer. These problems are especially commonplace
after strong geomagnetic storms because of induced currents which can disrupt
a lot of things besides the ionosphere.