Can't read files on backup CD

Helpline Q&A Directory

To free up some space I transferred my complete collection of photographic image files to a CD-R disc for archiving. I have successfully read from this disc many times, and have added to it and organised it into folders. I recently went to access the disc using Paint Shop Pro 5.0 and found that I could not read any files. They are listed normally in Windows Explorer, but open with a red cross in a box at the top of the page with a message saying 'this is not a valid BMP/Jpeg file'.

I have scanned the disc for viruses and it is clear. I have copied the files back to my hard disk, but I still can't read them. Have you any advice, particularly as to whether I have lost these photographs?

It's never wise to put too much faith in the infallibility of computers. Any data on a rewritable disc is at risk when you write to a drive. For example, whenever you save a file to your hard disk the data could be written to the wrong place, trashing the entire contents. This rarely happens, but its another reason for making backups. This means keeping at least two copies of important files.

With a normal backup, the backup copy plus the one on the hard disk equals two. But if you are archiving files to save space on the hard disk you should really make two copies on separate backup media. As you've found out the hard way, it isn't a good idea to keep just one copy of important files, wherever you store them. But, of course, none of this solves your problem.

It sounds as if the data contained in the image files is corrupt. However, it is worth making sure the problem isn't caused by a CD drive malfunction or a software fault - try to read the disc in another computer. But if the disc really is corrupted, there isn't much you can do.

As with a trashed hard drive, the data may well still be there, even though it is only recoverable by a data recovery expert. Search the web for 'data recovery' and you should find some relevant companies.

You could also try running the program CD-R Diagnostic made by CD-ROM Productions (www.cdrom-prod.com). It's a technical piece of software, though, and you can't use the downloadable demo version to recover files in earnest.

In our experience, and for future reference, Zip and Jaz cartridges are a faster and much more trustworthy backup medium.