Windows 7 is the latest release of Windows line of operating systems. A Windows 7 computer can become unbootable for various reasons that can affect the functioning of its earlier versions too, for example unexpected power failure. As the last resort, you might need to use your previous backup to restore lost data. But if a suitable backup is unavailable for any reason, you should use a windows data recovery product to recover it.

From: http://www.bestnewslinks.info/tutorials-howto/windows-7-fails-to-boot-post-power-failure/