Please ensure the following requirements are met, specifically the virutalization. Please also make sure you have installed the correct VirtualBox version.
Now runs on 32-bit and 64-bit OS (Windows XP, Windows 7, Windows 8 and Mac OSX)
Minimum 4GB RAM; 8Gb required to run Ambari and Hbase
Virtualization enabled on BIOS
Browser: Chrome 25+, IE 9+, Safari 6+ recommended. (Sandbox will not run on IE 10)