Installing Windows

I have an old Pentium on which I formatted the C drive. When I attempted to install Windows 98, the computer wasn’t recognizing the CDrom. When I tried to install a Win95 upgrade from floppy, I received a message stating that this was an upgrade and that no operating system exists. Without the use of the CDrom, I can’t install the Windows98 operating system. I have gone into the Bios and changed my boot sequence, but the CDrom still isn’t recognized. How can I get the operating system on the hard drive?