We came across an issue recently where we had an issue with our Hyper-V 2008 R2 server. The BOOTMGR file went missing on a reboot , all this was repaired by running Bootrec commands.
After the above the Hyper-V server would boot up however none of the VM’s would start and came up with the following error
“The virtual machine could not be started because the hypervisor is not running. The following actions may help you resolve the problem:
1) Verify that the processor of the physical computer has a supported version of hardware-assisted virtualization.
2) Verify that hardware-assisted virtualization and hardware-assisted data execution protection are enabled in the BIOS of the physical computer. (If you edit the BIOS to enable either setting, you must turn off the power to the physical computer and then turn it back on. Resetting the physical computer is not sufficient.)
3) If you have made changes to the Boot Configuration Data store, review these changes to ensure that the hypervisor is configured to launch automatically.”
The issue was that when we recreated the BCD store in did not set the Hypervisor to launch automatically.
We resolved this by running the following command “bcdedit /set hypervisorlaunchtype auto” after a reboot all worked fine