Windows 8/8.1 unable to turn off, restart, hibernate or sleep after upgrade

Fix Windows 8 and 8.1 Restart and Shutdown Problems by Disabling “Hybrid Shutdown” Feature.

There are many Windows 8/8.1 users who are complaining about various restart and shutdown issues. Many times their Windows 8/8.1 computers restart themselves as soon as the log in screen appears. Sometimes their computer systems hang while rebooting or shutting down the system.
Most of the times these kind of issues are related with the new "Hybrid Shutdown" feature introduced in Windows 8/8.1. Hybrid shutdown feature of Windows 8/8.1 decreases the total start up time by hibernating the kernel session instead of closing it which reduces the overall Windows loading time because resuming from hibernated system session is very less work compared to a full system initialisation.
But this new feature is causing problems to some computer systems and if you are also facing reboot or shutdown problems in Windows 8/8.1, you can fix it by disabling this new hybrid shutdown feature and doing a complete shutdown.
Just follow these simple steps:

1. If you are on new Start Screen, type power and Windows will automatically search for the term and will show you the results.
If you are on Desktop, move your cursor to top-right corner of screen to access new Charms Bar. Now click on Search option and type power in search box.

2. Now click on Settings link given in right-sidebar of search results page and then click on "Change what the power buttons do" link given in the search results as shown in following screen shot:



3. It'll open Power Options window. You can alternatively open the same window by typing powercfg.cpl in RUN dialogue box and press Enter and then click on the "Choose what the power buttons do" link given in left sidebar.
Now scroll down to bottom and you'll see "Turn on fast start up (recommended)" option given in Shutdown settings section as shown in following screen shot:




4. Disable the option by unchecking the check box and then click on "Save Changes" button.

PS: If the option is not shown or greyed out, scroll up and click on "Change settings that are currently unavailable" link.

5. That's it. Restart your system and your reboot or shutdown problems should get fixed in Windows 8/8.1

Easy and recommended method:

If the above solution doesn't fix your problem, you can try to execute following command in Command Prompt/cmd. Open Command Prompt as Administrator by right-click on the bottom-left corner and select the same option from the Win+X menu then type this command 

bcdedit /set disabledynamictick yes

The above mentioned command used to fix a very annoying freezing issue found in Windows8/8.1 Release Preview build. According to Microsoft the issue was fixed in Windows 8 RTM but if you are still facing the issue, you can try the command, It worked in my Windows 8.1 Enerprise N laptop.