Was this a Windows 7 backup image? If it was only made a month ago, could problems which caused you to reimage have already been present? I find that creeping corruption can begin right after install so keep a baseline image for cases like this.
You can try reimaging to see if it is a glitch with the operation or in the image itself. If this fail I would consider clean reinstalling following these steps to get a perfect baseline reinstall, then image it: Reinstalling Windows 7