M-Audio Prokeys 88SX No Sound!

I have an M-Audio Prokeys 88SX for years now. for the past few months the sound just goes away after playing for a little. There is no sound thru headphones either. Now it just wont come back. Some days, I turn it on, and play for a minute and it goes away. Than turn it off and on real quick and you can play for another minute. I am looking for any electronic help, I already tested some of the components inside but I have no direction. The keyboard looks like the first day I bought it. I do not want to just throw it out without trying. Any help will be appreciated.