Is this with just on particular .xls file or with any/all that you try to
format a cell in?
If it's just the one, then probably that file has been corrupted.
If it is any/all, then most likely part of Excel has gotten hosed up.
Usually that can be fixed by reinstalling Office/Excel and choosing to repair
or repeat last installation from the options presented.
A remote possibility would be that one of your RAM chips has gone bad, but
that would most likely cause problems in other applications besides Excel.
