A locked memory card means that you can't write to it (take more pictures) but you should be able to read the files off of it. If you can't then there is something else wrong.
I was able to repair an SD card with the lock slide that fell off. I cut a 1/8" piece of a paperclip and scotch taped it into the area where the slide was (in the unlocked position). I hope this helps.
Craig, August 2010