Midi keyboard recognized, but no signal

I'm the owner of a M-Audio Keystation Mini 32. When i plug this keyboard to my Macbook Air (bought in 2017) the keyboard is recongnized but there is no signal. It is connected when i go to System Report and USB. When i open the midi controller, i only get a signal for a few seconds when i refresh it, or when i start a new configuration. I have MacOS 10.13.2 running on my Macbook air. I've tried it also on a iMac wich is not updated yet (MacOS 10.12.6). On the iMac it does work.


I've tried everything but don't know how i'll get it work on my Macbook Air. Can anyone help me out?


(Sorry for the not fluent English)