Left clicking anywhere on the spreadsheet before clicking "Format Cells" may
help.

"Andy S." wrote:

There are times when working on an Excel spreadsheet (Excell 2000) and I
select "Format Cells (whether off of the tool bar or "right click"), the
format cells dialog does not display and I cannot format the selected cells.
Usually I have to shutdown the computer and re-boot. Sometimes even that
doesn't help.