Old Imports ?

So i'm still learning my way around but my question is this:

I have a bunch of memory cards, some of which have some of my own photos on them, when I put them into the card drive, and go to import the photos to lightroom, they a;; disappear. Even when i hit "all photos" as opposed to "new photos" Now, id like to edit my photos and whatnot, but i cannot seem to figure how to get these photos to import to lightroom.. help?