Sandbox in VirtualBox does not boot centOS

I have virtual box and downloaded Hortonworks Sandbox for VirtualBox from their website. When I start the machine I get two options fro CentOS Linux, both of them gets stuck with and nothing happen after selecting either one.
In tutorials, I noticed that when the machine start, it shows a message that indicate it booting CentOS.

Can you please guide me what shall I do?

You might not have allocated enough resources on your laptop to run virtual machine.