Keyboard Doesn't Light Up
 

Sometimes when I open my keyboard to text, my keyboard doesn't light up at all. Other times it's a little delayed, and other times its perfect. If I close the keyboard, slap the back side a little, and reopen it, it's usually fine. Anyone know what I can do to fix this?

My phone was originally from Sprint but has been flashed to Cricket, so I think taking it to a sprint store is out of the question, but I could be wrong? Any input? THanks.