I have downloaded OpenServer 5 from this link. I created a vm machine (Vmware workstation) and used this ISO file as CD-ROM image file(IDE). Everything works fine and the vm boots from CD-ROM normally and I can intall the OS, but when I try to write the ISO file as a bootable USB, my motherboards ( 2 different models ) don't recognized it as a bootable USB. I have used multiple programs to make the bootable USB like rufus and PowerISO with multiple different options with no success.
What is wrong here and what should I do?