How do I retreive pictures from external hard drive?

MY old PC worked slow so i put all of the *.jpg pictures on extrenal hard drive, about 80G worth of 12 years of family histroy.In the meantime my old PC crashed and then we bough a new one. When preparing to transfer these pictures from exteral hard drive to New PC, realized that all the pictures were gone!!!! Are they hidden? Or how can they be accidentaly erased?
And finally, any sugestions on how to retreive them?

PLEASE HELP