One version I know that always worked when I was working on the older stuff was Mountain Lion. You can still download this directly from Apple.
https://support.apple.com/kb/DL2076?locale=en_AU
Download the DMG file (disk image). You can then use something like TransMac to create the bootable installer if you only have a PC.
https://pureinfotech.com/create-maco...e-usb-windows/
You can then at least boot up off this using Option key, format the HDD as MAC OS Journalled, then Install Mac OS. You can then upgrade to High Sierra or create new boot media after you install everything.