I followed the instruction and did the installation. I realised then i had to enable the Virtual Technology in BIOS (which was enabled anyway). However, i still get the same error:
'Failed to Open a session for the virtual machine cloudera-quickstart-vm-5.4.2-0-virtualbox'
The virtual machine 'cloudera-quickstart-vm-5.4.2-0-virtualbox' has terminated unexpectedly during startup with exit code 1 (0x1). More details may be available in 'C:\Users\badao\VirtualBox VMs\cloudera-quickstart-vm-5.4.2-0-virtualbox\Logs\VBoxHardening.log'.