One way to enter safe mode in windows 10 is to boot from a Windows install USB or CD (pressing esc at boot and choosing that device if not automatic) and after the first screen selecting the language choose "repair your computer", than "troubleshoot - reset your pc or see advanced options", select "Command prompt"

in command prompt enter:

X:\Sources> bcdedit /set {default} safeboot minimal

exit command prompt

click on Continue (exit and continue to Windows 10)

to disable the boot in safe mode you do the same steps but use the following command:

X:\Sources> bcdedit /deletevalue {default} safeboot