hi,
http://blogs.msdn.com/b/volkerw/archive/2007/05/21/hardware-virtualization-check-utility.aspx
how about trying the http://www.grc.com/securable.htm by Gibson Research Corp sort of third party tool to check for VT-x support.
if you see Locked on, then the bios doesn't really switch on the VT-x (time to grab latest bios then)
if it is big "Yes", then according to virtualbox forum thread here,
https://www.virtualbox.org/ticket/10694
https://forums.virtualbox.org/viewtopic.php?f=8&t=48660
there are possibility another application to switch off VT-x? maybe,