Samsung NP940X5J-K01US - Manual (Page 91)

Troubleshooting
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Select Recover. Recovering to factory default
Recover the computer to factory default settings. If necessary,
back up important data to an external storage device before
restoring the system. See Backing up the current system.
1
When the computer starts Windows: On the Start screen,
click at the lower-left edge, and select Recovery.
When the computer does not start Windows: Turn on the
computer and press the F4 key several times before the
Samsung logo (Samsung ATIV) appears.