Weird hum - Yamaha P-250

by Val
(NYC)

Hello! My Yamaha P-250 developed a hum, seemingly overnight! One of my students was messing around with the buttons a lot and the following day I had a weird hum, not really coming through the speakers, but in the keyboard itself. Also, the window that lights up when you turn on the keyboard, has strange little black boxes that were never visible before.
Anyone have any suggestions??? PLEASE!!!
Thank you,
Val