Enable Virtualization in BIOS if my computer isn't giving me the option

Firstly you need to check if your computer supports virtualisation. You can do that at http://ark.intel.com/ (I'm assuming it's Intel, look for your CPU and check if the VT-X feature is present). Alternatively, you can download and run the Microsoft® Hardware-Assisted Virtualization Detection Tool.

If your computer does supports it, and you have checked every option in the BIOS, and your BIOS is the latest version (go to your manufacturer's website), then the only option is to flash a BIOS. The most popular site would be https://www.bios-mods.com/. Look for your computer make and model + BIOS version and follow the instructions there. Unfortunately this is the only way since your manufacturer did not add the option to enable virtualisation in the BIOS.

I ran into the same situation too - I have an Acer laptop and in my BIOS there's no option to enable VT-X (along with many others). In the end the only option was to flash a BIOS which has the options unlocked, but I decided against it as it was too risky- IT MAY BRICK YOUR COMPUTER AND RENDER IT UNUSABLE.

In conclusion, unless you desperately need virtualisation enabled, it's better to leave it as it is. Some manufacturer's just don't include the option in the BIOS...

EDIT:

I just upgraded from Windows 7 to Windows 8.1 Pro. When I was in Windows 7, VT-X was disabled and due to the lack of options in my BIOS, I couldn't use it. After upgrading, apparently VT-X was enabled (though the option still isn't in the BIOS) and now I can use the feature now! Yay! :)