The reason Skylake has problems with Windows 7 is because they removed the EHCI protocol from the USB controllers and only support xHCI from here on out. Windows 7 does not have any xHCI drivers by default, so they need to be slipstreamed onto the image if you're installing it through a USB stick. If you have a SATA DVD drive and install from the DVD, it should work fine, provided you have a PS2 mouse or keyboard, USB mice and keyboards won't work until the xHCI driver is installed, which would be included on the motherboard's driver DVD.