First use your finger to make a sliding motion from bottom to top on the illuminated screen in Modern UI, then click once All Applications. If you are using a mouse, please right click once All Applications.
Then on the command command prompt character use your finger to slide from top to bottom, and click once more Executable by system administrator. If you are using a mouse, click on the command prompt character and right click, then click once more Executable by system administrator.
If there is user account control, please click once yes.
Click to input Bcdedit /set {bootmgr} displaybootmenu yes,when completed press the Enter key on the keyboard. If you need to cancel the prompt to enter options at startup, simply change Yes to No.
Once completed, please restart your computer, then press F8 to enter setup screen upon startup, then press F4 or 4 to enter safemode.
Source:
http://support.microsoft.com/kb/2809468
