Why won't my DSI XL turn on

My DS is fully charged and the last time I was on it it worked fine. Then I try to get on it today and when I turn it on the bottom screen will light up for barely a second. I know it's not because of the charging the orange light is lit up because I'm charging it right now. It's not because I dropped it because I haven't. Is not because any water has spilled on it because it hasn't even been near food or water it has literally been sitting on my desk for maybe a month now. I tried to turn it on with it charging and without it charging so I know it's not water damage, charging or the battery is shot. If someone can tell me what is wrong and how to fix it then I'll be the happiest person in the world