Why is the right side of my top screen white?

I just bought this DSi on ebay a couple weeks ago, and it's been doing good. I keep it in my pocket most times when not in use. I went to a newphews birthday party and did a jump rope game with them. No rowdyness besides that, it wasn't droped or stepped on or bashed into anything. Just did a lot of jumping. What could have made this happen and what do I need to do to fix it? I am willing to try anything with a step-by-step video or instructions. Is it fixable without buying anything new?