My iPad won't charge unless it's turned off. What's wrong?

my ipad (2nd generation) suddenly stopped charging. the charger is not the problem as it still charges my iphone. I then used my iPad charger to charge my iPad but it still won't work. I plugged it in my laptop and I get nothing. I can only charge it if it's turned off and I don't know why this is happening.

This happened to me months ago but for some reason it fixed itself. It's really frustrating especially since I barely use my iPad and now it's acting up on me.