And if the answer to Otto's question is "yes", then another place to look is
in:
<Tools> <Options> <View> tab,
And make sure that under "Objects",
'Hide All' is *NOT* checked.
Further, you didn't mention your version, but there is a bug in XL97, where
if you use "Freeze Panes" at or under the validation cell, the drop-down
will *not* display.