Help, my keyboard doesn't work!

If you have an older keyboard that has a PS/2 style circular plug (instead of the rectangular USB plug), you may be in a panic if you unplug it and plug it back in while your computer is running, because your keyboard won’t work!  Never fear, it’s a simple fix – restart your computer.  PS/2 keyboards have to be plugged in when the machine starts, and won’t be recognized if you plug them in later.  Newer USB keyboards don’t have this problem.