Why No "Format Cells" Choice Option Always ?

[Bob]

Hello,

Using Excel 2007.

When I select a Column of numbers, I usually see a
choice for "Format Cells"

At other times, for different Columns (also with numbers in the cells, I
do not get the Format Cells choice.

All that shows up as being selectable are:

Cut, Copy, Clear Contents

Why might this be ?

Thanks