Is your Win98 CD bootable ? u must make sure it first.
If it is not , u can make a boot disk from Start>Settings>Controll Panel>Add / Remove Programm.
And than click on "StartUp disk" tab menu and clcik "Create Disk" ... u put blank floopy disk into your Floopy Disk Drive and and then Reboot your Computer.
And in BIOS system , set the booting from FDD and then Restart your computer.

If it isn't work either, replace ur CD-ROM with other one or Replace the Win98 Disc with Other Bootable Disc... if that isn't work well .. i don't know what should i say.