it is an old PC of mine with some extra parts, that arent that recent. this machine has ran windows 7 with this boot process in the past.
Old systems run on MBR new systems run on GPT, it's an option you can choose in rufus or whatever you use, I'm not sure but it probably defaults to the new GPT option, it is also called legacy or secure boot.
You can check with your system BIOS to see if it had a legacy secure toggle or you check with rufus to make a new USB with the other option.
As everybody already told you, even if you get it to boot into the windows 7 installation it might not like the hardware and not be bale to complete.