Why won’t it boot to a new harddrive???

I have a PC with swapable drives. I run 2000Server, NT4 Server, 98, 95. They are all on seperate removable hard drives. I needed to rebuild my machine so I wanted to start with a new install of 98. Now the computer will boot right up with the 2000, NT or 95 drives. It will not however boot to the floppy for the install of 98. All it does is look at the a:\ and then says there is no boot partition. I have tried a new startup disk. I also have tried an NT startup. It is not a bios setting becuase I have made sure it will boot a:,c: then cddrive. I am totally stumped by this…it will not boot to the a:…give me some ideas. Thanks