Using Office 2000

I am regularly sent files in Excel format which have been extported from
database applications.

Everything seems normal except that when I right-click a cell and select
Format - Nothing happens. No Format menu opens. The same happens (i.e.
nothing) when I select Format_Cells from the format menu.

However if I go to another workbook and format a cell then it works as
normal.

Also if I copy a format using the format painter in a different workbook,
and then paste the format to a cell in the Problem workbook then the format
changes.

Can anybody tell me how to sort this Format problem out?

Thanks in advance.

George