When i import AX2012 VM to Win2008 R2 by Hyper-V, It shows a error message:

The virtual_machine could not be started because the hypervisor is not running

1, Check Virtualization option in BOIS, please insure all items of virtualization included CPU are enabled

2, When you install Hyper-V in Windows Servers, it automatically disables desktop features like Hybernation / Sleep.  Some people may have changed the Windows' Registry manually to enable those features by changing the 'Start' Value from 1 to 3 in  
Y_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\hvboot\Start = DWORD 3

Since you have changed the Registry value for "hvboot" to enable Hybernation / Sleep feature,  you will need to start the Hypervisor manually. Do this: Open Command Prompt window with Administrative privilege and run the following command

> net start hvboot