Hi Linderz and welcome to the Forum. Sounds like the problem is fairly serious
and the only solution is a visit to the Technics Doctor. If you have just bought it from a retailer, you may have recourse with them.
One thought which occurs to me - this could be caused by overheating. Does the fault only occur after it has been switched on for some time? Is the keyboard subjected to adequate ventilation ? I know the later KNs had a fan fitted internally, but can't remember if this applied in the KN2000.