Cloudera VM 5.13 not loading in vbox

[#1]

I installed cloudera-quickstart-vm-5.13.0-0-virtualbox on vbox and when I try starting the virtual machine,the centos 6.7 gets loaded and then there is nothing more than black screen.i have installed it for 64-bit and virtualize tion is also enabled.Could anyone please help me on this.I am new using cloudera VM.Thanks in advance

[#2]

how much RAM have you allocated ?