Vincent,
I have a Y3K and thankfully never had this problem. I presume you bought this used from a private party. I would start by making sure nothing is in the media card slot.

If that fails, you will have to go to your nearest Yamaha dealer. Try swapping the power supply with another one that you know is good.

If the problem is not the power supply, you might try downloading and reinstalling the Operating system. To do this you will need a media card. They are hard to find in stores, I suggest getting one from ebay.

If all else fails, it will have to be opened up. Maybe a circuit board became unseated during transit. You could try yourself, or rely on the nearest service center.

Good luck, keep us updated on your progress.
Ted