When your system shutdown suddenly due to power failure or you turned off it without closing any current program, will affect your system settings. Next time when your restart your system, it may get stuck or hard to recover any last program.
To avoid that, your system will show you some advanced boot option when you restart, one of the boot option is ‘last known good configuration’. Last Known Good Configuration stores important system and registry every time you turn your computer off and Windows shuts down successfully.
To run system in ‘last known good configuration’ mode,
1.Remove all external hard disk, CD etc and restart your system.
2.Press F8 immediately when your start restarting before the windows logo appears.
3.Select your operating system and boot option ‘last known good configuration’.
Now your system run which registry files stored when it was turned off successfully.