Intel Skylake (100 series)/ Braswell platform have no EHCI controller and they only have XHCI controller. However, Windows 7 does not have the native XHCI driver, so the USB devices cannot work during installing Windows 7.
If you want to install Windows 7 on LIVA MINI PC and Skylake/Braswell Motherboard, you should add the XHCI driver into Windows 7 image and generate a Windows 7 installable USB thumb driver.
ECS Windows 7 Image Builder can help you. Please download Windows 7 Image Builder follow the steps on the below file to get it done.
How to use
* LIVA Mini PC Kit/ LIVA X can directly install Windows 7 without this tool