It may have fallen victim to electrostatic damage.  This time of
the year, the humidity is often low enough so you get static zaps
reaching for things.

    Ideally, the camera (and everything else involved, such as the
computer which is reading it) would have metal touch-plates to allow you
to drain off the static charget before you reach for the CV card (or
whatever other form of digital media which you may have in mind).
Unfortunately, these days, many of the camera bodies have precious
little metal to which to safely discharge.  My Nikon D70 has (as visible
metal) the tripod socket, the flash shoe, the strap brackets, and the
lens mount (plus the D70 badge itself), and the shutter release
button and surround.  I have no idea how many of these are actually
connected to a common point within the camera body (and I have not yet
tested them with a low-current ohmmeter).  I would expect the shutter
release button to be grounded, and perhaps the tripod socket, and the
flash shoe. Anything else doesn't get any bets either way.

    And once you are holding the CF card (or other) and reaching
towards the socket in the computer or the card reader, do you think to
ground yourself on the computer's chassis? (And, in a laptop, it may also
be all plastic.)  So -- you risk zapping either the flash card or the
computer each time you connect.  (Some readers have a metalization on
the outside which may server the purpose.)

    *If* your media has suffered a static zap, I sincerely doubt
that any data will be recoverable, and that any attempt to format will
be successful.  And static damage will not leave any visible signs on
the outside of the card.  You would need to examine the raw chip inside
with a powerful microscope to see what has been zapped, and you would
need to know what a static damaged chip *looks* like.

    Good Luck,
        DoN.