3DS won't turn on, charging light turns off after a few seconds

Okay so my friend gave me this busted New 3DS (the non-XL model) and we fixed it except for one part, and I ended up frying the button board by being lazy and putting the battery in backwards while avoiding closing the case all the way to test it. I replaced it, everything worked fine, then I gave up on fixing the HOME button, and pulled out the foam I had been using to try to push the ribbon cable clasp down. As soon as I did that, it stopped turning on, and I'm getting the same symptoms as when I had fried the button board: power button doesn't do anything, charging light turns on but doesn't stay on for more than a few seconds. Battery had been fully charged when it had been charging.

It can't be that I fried the board again, I didn't do anything that could have done that. I'm not sure where to test it with my multimeter to see if I did blow a fuse somehow.