Chosen Solution
I recently did a repair of the bottom screen, while doing so I probably damaged the digitizer since the touch screen wasn’t working anymore, so I bought a new digitizer and I replace it with the old one, but after this repair once I turned on the console the blue LED turned on for a few seconds, then when the backlight turned on the entire 3DS shuts off with a boop sound, I tried reseating every flat cable, but to no avail. Please Help Me!
I once had a 3DS that did the same thing. I took it apart to see what I could find, and the cable that connects the top screen was broken. I believe that the 3DS checks all of the components while starting up, and if it finds something broken or inactive, it will shut down with a “Boop” sound. So, I disconnected my top screen (Without unplugging the backlight) and it worked just fine. I suggest that you check your top screen as well as your bottom screen for any broken cables. Also, since you have reseated every cable, try popping in your old screen and see if that does the trick. If so, your new screen is incompatible with your system.
