Most of the times these kind of issues are related with the new "Hybrid Shutdown" (also known as "Fast Startup") feature introduced in Windows 8. Hybrid shutdown feature of Windows 8 decreases the total startup 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 initialization.
But this new feature is causing problems to some computer systems and if you are also facing reboot or shutdown problems in Windows 8, you can fix it by disabling this new hybrid shutdown feature and doing a complete shutdown.
Just follow these simple steps:
STEP 1:
First of all you'll need to open Power Options window which can be opened using any of following methods:
a. Press WIN+R keys together to launch RUN dialog box and then type powercfg.cpl and press Enter.
b. Press WIN+X keys together to launch "WIN+X Menu" and then select "Power Options" from the list.
c. 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. 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 screenshot:
STEP 2:
In Power Options window, click on the "Choose what the power buttons do" link given in left sidebar.
STEP 3:
Now scroll down to bottom and you'll see "Turn on fast startup (recommended)" option given in Shutdown settings section as shown in following screenshot:
STEP 4:
Disable the option by unchecking the checkbox 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. It'll allow you to change the option settings.
STEP 5:
That's it. Restart your system and your reboot or shutdown problems should get fixed in Windows 8 and later.
NOTE 1: If the above solution doesn't fix your problem, you can try to execute following command in Command Prompt. Open Command Prompt as Administrator by right-click on the bottom-left corner and select the same option from the Win+X menu:
bcdedit /set disabledynamictick yes
The above mentioned command used to fix a very annoying freezing issue found in Windows 8 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.
NOTE 2: In some computers, you may also check BIOS settings. If it contains "Fast Boot" or similar option, disable it.
