How To Install Unity 3D Into Virtual Box Win 7

1) Install Virtual Box.

2) Create a Virtual Win 7 from iso.
You need to find an iso file e.g. https://blackeyez007.blogspot.my/2015/09/windows-7-tiny-unattended-fully.html

3) Set 3D Acceleration In Virtual Box Manager.

4) Run Virtual Win 7 in Safe Mode.
Refer http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/

4) Install Virtual Box Addition.
Tick Direct3D Support

If your Internet Explorer could not open websites despite live internet connection,  go to menu Tools/Internet Options... , and then go to the Advanced Tab and click Reset button.