Cannot install OS due to built in ethernet not working

So my little brother thought it would okay to install windows on my mac without using bootcamp. Now i can't seem to get the built in ethernet to work, I even tried using a usb to ethernet but to no avail(Linksys). I even put in a new harddrive, but that didn't work either.Tried booting with usb, but since i cant use internet it won't work. I also tried ctlr+Option+R. Does anyone have any ideas?