Fast Startup function works like hibernation. During shutdown of system, logged-in user session gets closed and system is going to be hibernated. As a result user obtains faster computer start.
Disabling Fast Startup function
Via Control Panel
To disable Fast Startup function you need to run Control Panel then choose category Power Option (or System and security -> Power Option) and next select Choose what the power buttons do.
In the next step, choose option Change settings that are currently unavailable and uncheck Turn on fast startup.
Via Command-line interface
Fast Startup function can be disabled also by cmd using command powercfg /h off (cmd has to run by Run as Administrator option).
If it would be necessary to start the function again, just enter the following command:
powercfg /h on
Via system registry
The next way to disable Fast Startup function is to change entry in the registry:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Power HiberbootEnabled DWORD.
Value 0 means that the Fast Startup option is disabled and value 1 that the option is enabled.
After disabling the Fast Startup function you have to reboot your computer.