Alright, here’s some detail. I got this DSi a few months ago from a close friend, but I’m just now getting to actually...

If it still isn't working, try "hotwiring" it. The power button connects to a small connector under the keyboard. To access under the keyboard, use an edge of a plastic card (an old credit card does wonders) to wedge under the top side of the keyboard. it should require a little work, but it will unclip with a popping sound. Now, carefully flip the keyboard upside down while moving it towards the mousepad. There's a connector for the keyboard there that wou wouldn't want to break. now, theres a connector on the top-right corner of where the keyboard was. using a small fllat-head screwdriver or other peice of metal, gently tap the two points on the other side of the connector. Your computer should turn on.