VT-x is Intel’s Virtualization Technology. If the error is reporting that it is unavailable then you may not be able to run the sandbox at all, not on that computer at least. There are some links and resources in this thread that you may want to take a look at http://hortonworks.com/community/forums/topic/host-does-not-support-intel-vt-x/
Can you give us the exact model of your processor? That will probably help with troubleshooting.