We had about 150 pictures

We had about 150 pictures on the memory card, took about 13 this weekend, showed them on the camera, but we think battery was low now the new pictures show as a file error. if I look at on a PC I can see the files but cant preview, also the size is about 800KB when old ones are about 3Meg. Have tryed several recovery utilitys but none see currupted photos. I think it is a bad index. Card is a sony 8GB stick Thanks for any help