Since, Z170 chipset and BIOS have no support for USB 2.0 Enhanced Host Controller (EHCI) mode by default.
But, our BIOS implement the workaround for it. Please follow the instruction below, then should be no problem to get USB KB/MOUSE to work.
a. Make sure the BIOS build date is later than 2015/09/10.
b. Enable this option under BIOS.
Path: USB Settings >> Install Windows 7 USB support >> Enabled