All of my past valid images are now corrupt

I have 2 desktops that are virtually identical except that one uses win7 64 bit and the other win7 32 bit. On both I have created images and restored from them several times in the past (using home 2010). They are not networked. A few days ago I tried a restore on one computer and got the message that it had failed because the image was corrupt. I then discovered the same problem on the other computer. I have tried many variations: run from windows and boot from the emergency disk, using images on internal and external drives, saved to "virgin" drives. I have also created new images which acronis said were successful and then when I tried to restore from that image acronis said the image was corrupt. Validate has said that some images were okay, but in a subsequent restore acronis said they were corrupt. Now validate says all images are corrupt, but if I run validate 2 times on the same image, the failure comes at different points in the test. That happens with restore too. I have run virus tests on both computers and found nothing. On one computer I ran Registry Mechanic which found many problems that I told it to correct, but that made no difference. I also cloned one computer's C:/ and installed the result in the other computer - the clone worked fine.