"New" 3DS XL with a lot of problems

Hello and thank you for reading.
Last Sunday I bought a second hand N3DS XL. It looked ok and I knew beforehand that it didn’t turn on.

Opened it up and cleaned, everything seemed right and also I did check the Micro SD it had inside, it turned out that the console was hacked and had Luma 9.x

Formatted the SD, created the necessary folders for luma (Used Luma 11.x bc that’s the version I had in hand) et voilà, Luma config screen!
My happiness didn’t last long since I got an Arm9 error when pressed Start for saving.

Right now I don’t have my flashcart so anything with magnetboot its out of question. Then decided to crossfingers and try ctrt, It worked!
Follow all the steps and got the n3ds working again, I could even update and did so.
Again, my happiness ended here. When I was on the final process of using Rosalina to inject HB on Download Play, it crashed. Got an Arm error again but I can’t remember if it was 9 or 11.

So, I thought that maybe updating luma to the newest version could fix it. First it didn’t turn on, just got the blue Led that turns on for a few seconds and then turns off. Pressed Start and got the luma config screen correctly. Everything seemed right and I was about to finish the process to install FBI but I had to do something and Turned off the console for the last Time.

After that, all I got is the goddam blue light that turns on for seconds then turns off.

Sry if it’s a lot of text but I want to give info 'bout all I did.
A few notes:
-Original owner told me that it did turn On normally and sometimes just the same blue light with the same behavior.
-When I was cleaning it, I did noticed that the flex that connects the motherboard with the power board (the one with the battery, pw button, C-stick, etc) had a visible crack from side to side (transversal). I did check it with a light and didn’t look like any trail were damaged, but it can be.
-Followig the condition of the flex, when I hit a very little the Mobo, the console freezed or went black.
-At some point I got it working using pressure against the flex and its connector.

Is there a way to tell if the problem is in the motherboard or the flex I mentioned?
Maybe I can get my flashcard on Wednesday to use magnetboot.

On the other side of the flex connector is the Wifi board (shielded) and the Nand (unshielded). Is there a way to tell if the nand isn’t working? :c

Thank you a lot for any help.