That message means that the computer is looking for info on the floppy drive (presuming it has one). The main drive is normally the "C" drive. It sounds like when you removed the battery, it reverted to the factory settings when powered up again.
First thing to look at, when it starts booting, do you see at the bottom of the screen,something like "Enter setup.Hit Del"? If so, you could try doing this, find the bit where it says "Boot sequence" and change it to boot from the C drive 1st, instead of A.
If you can't do that, when you get as far as you did before, ie at the "A" prompt, type C:\ and hit enter. This should change it to the drive where your operating system(OS) is(presumably a version of windows), and bring up a list of files/programmes on that drive. From there you should be able to find your OS and start it from there, but try the other thing first.
Hope that helps, it's difficult, not being able to see the computer to see what's happening.