A: Windows 8 introduces a fast, new startup capability, which, because of several improvements, allows Windows 8 to start faster than an equivalent Windows 7 system. One of the changes is the saving of the kernel session to disk (which includes device and system service state) when the machine is shut down and then reading it in at system startup instead of reinitializing all system components and drivers.

This saves a lot of time, speeding up the shutdown and startup. This kernel session is saved in the hibernation file (the same place used if a full system hibernation of a running system is saved). If you disable the hibernation file using a command such as  the following (from an elevated command prompt):

powercfg /h off

then the hiberfil.sys is removed and there is nowhere for the kernel session to be stored. This means the fast startup process usage of a saved kernel session isn't possible.

To fix, re-enable hibernation to enable Windows to create a new hiberfil.sys and allow the saving and restoring of the kernel session:

powercfg /h on

Learn more at "Grocking the Windows 8 Start Menu" and "What is the Stardock Win8 Start utility?"