In Short -> You must enable VT-x Technology in your BIOS.

Here are the detailed steps:

1- Restore Optimized Defaults (Not Necessary)//Steps to start BIOS

  Its better to restore Optimized Defaults before, But following steps are 
  not necessary:
  Reboot the computer and open the system's BIOS menu. This can usually be 
  done by pressing the delete key, the F1 key or Alt and F4 keys depending 
  on the system.
  Select Restore Defaults or Restore Optimized Defaults, and then select 
  Save & Exit.

2- Enable VT-x Technology in BIOS (Necessary)

  Power on/Reboot the machine and open the BIOS (as per Step 1).
  Open the Processor submenu The processor settings menu may be hidden in 
  the Chipset, Advanced CPU Configuration or Northbridge.
  Enable Intel Virtualization Technology (also known as Intel VT-x) or 
  AMD-V depending on the brand of the processor. The virtualization 
  extensions may be labelled Virtualization Extensions, Vanderpool or 
  various other names depending on the OEM and system BIOS.
  Select Save & Exit.