Wired keyboard not found

I'm using the Apple wired keyboard with num pad which I connected to my 27" Cinema Display. When the Mac Pro (mid 2010) was shut down, and I start it, the Mac can't find the keyboard. Instead, it opens a bluetooth window, saying that no keyboard could be found. The wired mouse is connected to the Cinema Display as well and there's no problems.

I have to unplug the keyboard from the Display, then reconnect it, and sometimes I have to do this 3 times for the keyboard to appear. What's wrong here? I sometimes also have to plug it into another port of the display. But it can't be the ports/the display I think, because the mouse has no problems.
So I thought it must be the keyboard. But it can't be the keyboard because when I directly connect it to the Mac, it instantly appears.

Anyone know what this could be?

I swapped ports, read my post I can't really keep the keyboard plugged into the Mac because it's too far away. But I'm not even sure if it works instantly when plugged into the Mac, it may just have been a coincidence.

I checked the permissions, they seemed to be okay. Hmm…