Not sure if you are still having issues, but from what you said with the blue light fading out it sounds like an exploit was used on it called arm9loaderhax, in which case the system will refuse to boot without that file on the root of the sd card. https://github.com/AuroraWright/Luma3DS/... If you download this and put the included arm9loaderhax.bin file on the root of the sd card, and then after inserting the sd card back into the 3ds try to boot it it should work
Its either the screen,camera, or speaker ribbon cables. Either they have come loose or have become damaged. Reseat/replace cables to fix. The 3ds checks all the hardware, and if something is not detected it will turn off/not turn on
Might possibly be damage to the ribbon cable or the top screen, but from what you have said i would venture to say that the ribbon cable has come loose on one of the sides, either on the lcd or to the system. Might involve replacing the top lcd.