koala

If they were transferred from the camera in the default format and then coverted to jpeg, then possibly the conversion was faulty. But that wouldn't explain how they were fine one day and now damaged. Are these the original unedited files?

It could be a problem with the hard drive. Have you run the manufacturer's diagnostics utility to find and possibly fix any errors?

Is this the only problem or are any non-photo files damaged? Any program crashes or other system problems?

If you know your way around Photoshop, you could fix them. It would just take a few minutes for each one if they're only sliced, a bit longer for colour corrections. Or you can contact freddyhard or me and we'll have a go at fixing them.