Probably the memory card is corrupted..its a bit of a thorny issue trying to fix images and a lot of the sofware used is not free.
There are people about with a lot of technical skill with images,try and get one of them to play with yours,or hopefully someone more
knowledgable than me will chip in.
You could try running the images through this freware and see what it does (dont know how many files it will let you recover for free)
Also worth a try
Couple of threds here with ideas
A lot of threads suggest IrfanView image viewer will sometimes open files others see as corupted,might be worth a shot.