If you've got a USB keyboard, I suspect that AC may well have identified the problem. (You can buy a PS/2 keyboard for about a fiver from Tesco, or simply borrow one from a friend).
If that doesn't work, try booting from a boot-up floppy instead of your Windows disk.
(Incidentally, if you can eventually boot properly into the screen which allows you to reformat your hard drive, it's worth trying to install Windows on top of itself before actually formatting the drive. I've solved loads of problems with 'on top' installations of Windows, which preserve all software and data, without the need to format the drive first).
Chris