Grayed-out File Sharing

My laptop and desktop had been set to share files w/ each other at home and
that worked just fine - until we went on vacation. When I wanted to pick up
my e-mail at a hotspot (is that the right term?), the ISP recommended that I
disable file sharing. Made sense, so I did. Now I'm home and can't get file
sharing turned back on. Actually, the box is checked, but grayed out. How
do I go about correcting this?

Thanks,
--
Rich