try removing the INLINE CSS of the child ULs, they are set to "display:none;". Since inline CSS generally overrides any stylesheet, your rule won't apply. Tho actually you can add display:block ! important; to your :hover rules, but that is messy.
ALSO, I noticed you have overflow:hidden; on your #topNavList, probably used to contain your floats, but this also has a the unfortunate side effects of hiding your drop downs as well.