Bought used computer, cable issues

So we got this really good used computer, everything set up, but when we plug in the Mouse and Keyboard, they will not work. No lights, or reaction upon startup.

We attempted fidgeting with it, but to no avail. The previous owner said he was able to get those to work previously (he got a new computer so no longer needed the one he sold.)

Are we missing something? A cable in the wrong place? I havent dealt with that particular part of the computer so I'm unsure of what should be done.