Same problem with my dads laptop worked fine on Windows 8 just 8.1 causing the issue.
The problem is caused by Hybrid boot. If you noticed when you restart your system via restart button you will notice it will always boot without fail since restart does not use Hybrid boot.
Since I use a SSD I see little need for Hybrid Boot. You can disable this by disabling the Hibernation File. This will make your bootup longer but only Windows 7 speed bootup.
http://www.maketecheasier.com/disable-hybrid-boot-and-shutdown-in-windows-8/
The Above link will set you straight and make your system always boot up 100%.
I myself just disable the Hibernation File since I see no need for it since I use a SSD.
I don't know if this is a bug and needs a fix but I recommend you disable till Microsoft offers a fix. I think older systems are more at risk than newer ones to this system hang. By the way you don't need to shut down the system when it hangs just press the power button once and it comes out of hibernation then just log in as normal.
Hope my post is useful.