Until recently I have been getting successful scheduled daily backups to an external drive under Windows 7 (Home). This backup included a system image. For space consideration I had set the backup to only include the most recent system image. As a result of a virus problem, the most recent backup has failed, indicating the backup volume shadow service was unable create or perhaps save a system image. What I need to know is whether the previous, untainted system image ctreated by an earlier successful back has been overwritten by this failer. In other words, if a Windows Backup fails, are the previous successful backup images intact, or are they compromised or overwritten, in part, by the incomplete or failed image. I want to restore my system from the "old" image but am nervous that it may no longer be valid.

you could try navigating to the backed up system image and check the date stamp for the largest file in the folder (this is the image) and see if it has same date as the failure or if its a previous date. I hope the image is OK for you. Worse comes to worse you can just run it and see what happens, system is already corrupt according to you, worse case... you get exactly same image you have running now, best case, it failed without touching the main image and all is good with the world.Please remember to flag a post that helps you as "answer" so that it may help others with same problems.