When you replace a bootable HDD with a bootable SSD, your boot configuration may not get copied over.  The default boot configuration may not load hypervisor.  

You will get this error from Hyper-V Manager when attempting to start a Hyper-V machine:

An error occurred while attempting to start the selected virtual machine(s).

‘COMPUTERNAME’ failed to start.

Virtual machine ‘COMPUTERNAME’ could not be started because the hypervisor is not running.

To change so hypervisor loads:

  1. Launch command prompt as an administrator
  2. Execute bcdedit /set hypervisorlaunchtype Auto
  3. Reboot

That’s it.  Your previously working Hypervisor virtual machines should be back up and running.