External USB keyboard no longer works

Your message would be easier to decode if you had proofread it before posting.

Does your keyboard work when the mouse is plugged directly into the computer instead of into the keyboard, or does the keyboard not work at all? If not at all, then it sounds as though you're right in guessing that the keyboard isn't getting power for some reason (bad cable? bad connection inside the KB? USB port on computer shut down?) If the KB works when the mouse isn't plugged into it, then the mouse and KB together are demanding more power than the computer's USB port can supply, and neither is getting what it needs when the mouse is connected to the KB. In that case, plug the mouse directly into the computer to use it.

The USB port in your keyboard probably doesn't put out enough power for the mouse you are using. This is typical of older keyboards, which were designed to power old-style electromechanical mice rather than the laser mice that are commonplace today.