I wholehartedly recommend that you install W10 instead. You can use your 7 key while teh free upgrade offer is available(until the 29th). It's a far better OS and mandatory if you game as DX12 is exclusive to it.
Assuming you are on an intel platform, these are the steps you should take for optimum results:
Get the latest drivers from here:
https://downloadcenter.intel.com/download/25165/Intel-Rapid-Storage-Technology-Intel-RST-RAID-Driver?product=55005
File: f6flpy-x64.zip. Unzip it to a folder on a USB drive(it can be teh one with windows on it).
Disconnect all the drives except the one you're installing to, then go into the BIOS and under "boot" disable CSM and enable "secure boot".
Start the install and when it asks where to install hit "have disk" and point it to the folder you put the above files in.
then hit shift +f10 then:
diskpart
list disk
select disk x(x beeing the drive you are installing to)
clean
convert gpt
exit
exit
then hit refresh and select "create" to make a partition for windows as big as you require it. windows will create several partitions and auto-select the proper one to install to.
WARNING: this will erase all partitions and data on the drive