Best way to install Win7

Hello,

So I bought a custom build beast with "GIGABYTE X79-UP4 ATX w/ Ultra Durable 5, GblAN, 4 GEn3 PCIe x16, 2 PCIe x1, 1 PCI" as a mobo, and it came preinstalled with an UEFI bios. No matter what I do, USB drives with Win7 on them won't be seen in the boot menu, which is scarry. I tried many things, like formatting into a FAT32 file system with Rufus, and placing a GPT layout... still nothing.

I gave up on USBs and burned the Win7 image on a DVD, and tried booting from that. It worked, Windows started loading necessary files... then it crashed saying it didn't find a specific file...

I used this ISO repeatedly before, there is nothing wrong with it, but this new desktop is killing me... nothing works.

Any ideas? How do I remove the pre installed Win8 and replace with Win7

Thanks