Virtualbox: VT-X is not available
In some cases when you try to get a virtual machine running with Virtualbox or similar virtualization software you will get an error stating that 'VT-X is not available'. This relates to BIOS settings which, depending on your processor, determine whether your computer is able to virtualize stuff. These settings are not set automatically however, so it's worth a look into your BIOS whether you can actually change the setting and if your processor allows it.
The keyword to look for in the settings is 'Virtualization', it's probably placed in some advanced tab if there are some of those in your BIOS.
To see how it's done with a Z77X-UDH3 motherboard by Gigabyte see this post: Gigabyte Z77X-UDH3