There could be a number of issues with that , but the most likely is you should go to your system BIOS and turn on Hardware Virtualization, it is generally required for majority VM environments .
And I would suggest that you use VMware (http://www.vmware.com/) rather thn VirtualBox , as VMware is more stable and faster in comparison to Virtual Box.
Let me know if this solves your issues, will explore more if not.