Intermittent mouse/keyboard recognition

I am running Windows XP and am having the following problem.

Every other time I boot up the system, my mouse (PS/2 connector), and the keyboard will not work. The mouse doesn’t show up in device manager, but the keyboard does. There are no apparrant conflicts with the keyboard, it just
doesn’t work. Each time, I have to plug in a USB mouse, and reboot the machine for it to recognize the PS/2 mouse, and for the keyboard to work.

Does anyone know what the conflict might be, and how to resolve it?

Thanks,
Kevin