Why does my casio keyboard keep turning off?

think the person I bought it from whom had kids must have dropped it or something. It is a $300 keyboard and I paid $50 for it. I thought it was the batteries and that we needed to buy a new adapter for it since the adapter was broken, which makes me now wonder about the keyboard. When we turn it on and try to play it , it plays like this crackling sound, and then often if we play several keys at once it'll just cut off. Anyone know what the problem could be?

I ased this last week, but I only got one two answers that didn't help very much