Damaged Files

apologies if this is posted in the wrong section, i'm a first time poster here.

Anyway, i recently updated the operating system on my PowerMac G5 from 10.3 to Leopard and backed up the files accordingly, most of them PDFs, Jpegs, Illustrator/photoshop EPS onto a portable hard drive.

Now when i try and open the files i recently backed up, i get the followingg messages:

"There was an error opening this document. The file is damaged and could not be repaired"

"The acobat PDF file is having difficulties. The file is damaged and could not be repaired"

I've tried opening the files in various versions of the relevant applications.
I suspect that said files were damaged when i backed up, is there any way i can save some valuable artwork on these files by repairing them or am i truly screwed?