About the speed of a serial communication, you must have the 2 devices connected using the same speed for comunicate. You can select it on the computer, but not in the keyboard.
In fact, the keyboard adapt it speed to the speed you choosed in the computer.

You have to test on another computer. If it doesn't work, ask to your ketron deeler to test this cable with anoter keyboard...

I think you will have a good diagnostik.