D70 Nikon (by 2 users)

Difficult to say without seeing whats going off, your best bet is to stop using the card and get a memory card reader its quicker and better, and all your pictures may just be there and formatting the card may solve the problems..

if all is still not all right (prior to formatting the card) the card may have a fault or be corrupted (assuming the camera is ok)

There are many programs that can help you recover faulty formatted or corrupt memory cards. Do a search on google and try a few as some are better than others and some work better in certain situations than others.
searches to try
memory card recovery
memory card repair
Corrupted Memory Card

I wish you the very best of luck..
If I can be of further help drop me a line