Laptop will not boot

My client has an old Trogon laptop, from I would say 1998 or so. It had Windows 98 (not SE) and a 2G or 4G hard drive. The hard drive was going bad, and the floppy drive was destroying disks. So I bought another Fujitsu 6G hard drive and an externalUSB floppy drive. The laptop comes up fine, and I can go into BIOS to see that the cd-rom, floppy, and hard drive are detected. I want to boot to either the cd or disk to install an OS, but even if I set the boot order in the BIOS, the only message I end up with is “Operating System no found.”

What am I doing wrong?!