Excel locks up

Has anyone ever had the following problem in Excel 97 or 2000? What happens is that the highlight (selection) is turned on, and it is impossible to turn it off. I’ve tried F8, Alt-F4 to close the program, ESC, etc. But nothing on the keyboard works.

Basically, Excel locks up except for the mouse continuously highlighting. It’s weird because it has never happened to me at home. It only seems to happen to students that I teach in a classroom of networked computers (Windows NT network withWin98 OS).