Toshiba Satellite U840 Series User Manual page 78

You can not use System Recovery Options if restoring the pre-installed
software without System Recovery Options.
When you reinstall the Windows operating system, the hard disk will be
reformatted and all data will be lost.
1.
2.
3.
User's Manual
Turn off your computer.
While holding down 0 (zero) key on the keyboard, turn on your
computer.
A menu will be displayed from which you should follow the on-screen
instructions.
Satellite U840/U800 Series
4-24