You must enable Hardware Virtualization (HV) before you use vSphere Fault Tolerance.
When you attempt to power on a virtual machine with Fault Tolerance enabled, an error message might appear if you did not enable HV.
This error is often the result of HV not being available on the ESXi server on which you are attempting to power on the virtual machine. HV might not be available either because it is not supported by the ESXi server hardware or because HV is not enabled in the BIOS.
If the ESXi server hardware supports HV, but HV is not currently enabled, enable HV in the BIOS on that server. The process for enabling HV varies among BIOSes. See the documentation for your hosts' BIOSes for details on how to enable HV.
If the ESXi server hardware does not support HV, switch to hardware that uses processors that support Fault Tolerance.