I have a old PC With CPU : i3 3.1ghz and 8 GB RAM DDR3 and 128 GB SSD and 250 GB hhd i can't proxmox installing at the First step in booting write. '/Dev/sr0' for ISO and '/Dev/sdc' For ISO
Are you installing it from a bootable USB-stick? Looks like your boot media isn't right. If yes try another computer and tool like dd to write your install media.
