This is something that has been bothering me for quite some time as I cannot use Windows 8 for any video playback after installing Hyper-V 3.0. Found a workaround though and even if it requires a reboot, it shouldn’t be a problem if you are running on a UEFI system. The workaround is to disable Hyper-V via BCDEDIT. At an elevated command prompt enter the following: “bcdedit /set hypervisorlaunchtype off” and reboot. Keep in mind that if you want to use Hyper-V again you must run “bcdedit /set hypervisorlaunchtype auto” once again.