Disable fast startup in:
Control Panel
Power Options
Choose what the power buttons do
Change settings that are currently unavailable
deselect [x] Turn on fast startup

Start an Administrator CMD prompt:
C:\>bcdedit /set {default} bootmenupolicy legacy
C:\>bcdedit /set {bootmgr} Timeout 10
C:\>bcdedit /set {bootmgr} DisplayBootMenu true