No sound - Yamaha PSR-GX76

(Oregon)

My son is interested in learning to play the keyboard and we just borrowed a PSR-GX76 from a family member. We plug in the power cord and turn it on. There is a orange box in middle that lights up with a picture of a keyboard on it. We get no sound out of it except when you initially turn it on..you can hear a slight speaker noise. No matter what button you push nothing changes on the screen in the middle. No sound. When you push Demo...nothing happens. Any input would be much appreciated. My brother-in-law said he thinks this happened to him before but does not remember what key he pushed.

Thanks from an anxious-to-learn player in Oregon