Seems they are corrupted. Put on a USB-stick and try on a different computer to confirm that conclusion. Let's hope they show up well there. Then it's a problem with your irfanview or Windows.
Also try to open a few of such files from your backup harddisk. What happens?
Once you've got a better diagnosis, you'll find the best solution, I trust.
sorry but please help a total computer n00b.
recently my pc was infected with a virus and i had to get windows xp reinstalled.
the repair man kindly backed up my picture and video files of the family. the movie files are opening and playing as they should but my pictures files are not
the folders show small thumbnail pics but when i open the folder i cannot preview any of the pictures. the are all saved as JPG files.
the message that comes up when i try to open with irfanview is
Can't read file header !
Unknow file format or file not found !
please help me as i have some pictures of my new born daughter taken 3 weeks ago and have not backed up onto an external harddrive.