I have a lot of photographs stored in various folders as jpegs (with XP Pro). Now all the thumbnails have disappeared. If I try to view a photo in Picture and Fax Viewer I get "No preview available". If I use Paint I get "This is not a valid bitmap file, or its format is not currently supported". If I save one of these files to a floppy and try to view it I get the same thing, but new jpegs saved to the c: drive are fine.
After looking at some related threads I did an error-checking exercise (My Computer, right click on C: drive, Properties, Tools). This looked promising - text appeared saying something like "Windows has replaced a bad cluster" for every jpeg - but the problem is still there. The only difference is that each folder now contains a new file called "Thumbs".
This all started when I tried to back up the files to a DVD-R. Windows created a temporary file ready to transfer but couldn't recognise the disc. I gave up, deleted the temp file, went back to the main Pictures folder and noticed two odd files that hadn't been there before. One might have been called Thumbs. I deleted them, which is when the trouble began.
Sorry to go on. All suggestions gratefully received.