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.

For instance, suppose you have a Windows 7 run desktop computer. You encounter a power failure when the computer is in sleep mode. The next time, when you try to boot the computer, you observe one or more of the following behaviors:

The startup process fails
You come across a black screen
The computer directly enters into repair mode

Cause
The above situation can occur if the computer is set up to enter the hibernation or hybrid sleep mode when the power goes off. The hybrid sleep mode is enabled on desktop computer by default. So, if the computer is in sleep mode when the power outage occurs, it actually enters in hybrid sleep mode.

Unexpected power outage can even result into corruption of any critical boot files, file system structures or operating system files.

Solution
To solve the discussed issue, you should boot your computer using a Windows 7 installation DVD or Windows PE (Windows Preinstallation Environment) disc. You can then try to start the computer in normal mode.

If this fails and your computer still cannot boot, you should use Windows RE (Windows Recovery Environment) to run tools like:

Startup Repair
System Restore
sfc /scannow command
bootrec /fixmbr command
bootrec /fixboot command
bootrec /rebuildbcd command
chkdsk /r command

If these measures prove unable to solve the described problem, you should finally opt for a windows partition recovery solution to recover the inaccessible data. However, you can reinstall the system provided a good backup is available. A windows data recovery software can scan the corrupted disk and recover the lost data at a safe location.