“Fast Boot” is some sort of new “hybrid shutdown” feature that Redmond came out with in Windows 8, but since no one used that stub of crap, everyone (myself included) thought it was a new feature in Windows 10. Either way, it’s a great feature that really speeds up the boot time through some sort of Windows OS magic! In my copy, it was turned on by default, but just in case yours isn’t (or just to ensure that it is), it’s a fairly simple task to enable fast boot in Windows 10.
Ask Cortana for Power Options (in other words, type “power options” into the search bar; it should be the first result). You can always navigate Control Panel -> All Control Panel Options -> Power Options.
On the left sidebar, click “Choose what the power buttons do”.
In the “Define power buttons…” dialog, click the “Change settings that are currently unavailable” option.
Under “Shutdown settings”, make sure the fast startup option is checked.
Save settings, close, and you’re all set!
Source: Redmond Pie