mobile

Hi all,
This is The premise:
My note 10.1 has been a good companion for an year and an half now, and i always kept it in good shape.
However, since december the battery just stopped charging as it used to.
To simply put it, it just took a lot to charge (as if the tablet didn't receive enough energy) and the battery drained at insane speed.
Not knowing what to do, and having a void warranty (i know, sucks, but with the vanilla p600 i coulnd't even open the pdfs i use to study, so it was useless to me ) I just had to bring it to a local repairman who is affiliated with samsung. They immediately ruled out the possibility of it being the battery, and they said it was probably something related to the simple connector, that they changed with an original one.

Now the real trouble:
After they gave it back to me, the tablet can't go 5 minutes without the screen flickering like crazy and then rebooting.
I tried different ROMS, thinking it could have been something related to the Ios. CM12, Hyperrom p600, the vanilla Rom that was originally in my tablet and so on.
The big problem is that this unnerving flickering and rebooting is not tied to the ROM, as it happens even when i'm just using TWRP (version 2.6.1.1).
To be more precise: the tablet in recovery mode is fine and nothing happens if i do nothing with it; however the screen starts flickering and the tablet reboots the moment I attempt to flash something, or even everytime I do a factory reset.
Now the situation has worsened: to simply put it, I can't no longer access the tablet with any rom, be it vanilla (touchwiz) or android-stock based.
What could possibly be the reason behind this problem? I guess it has nothing to do with software issues (i have the vanilla 4.4.2 installed right now, but it can't even finish the setup).
Is there any advice you can give me?
To be more precise, the flickering is not like there is some intermitting bright light or anything: it's like the tablet's screen turns off and on very quickly for 30 seconds, and then just reboots.
After a lot of tries, i managed to install the unofficial cm by temasek for note 10.1 2015, but the problem keeps popping up with every rom I tried.
Regarding the kernel I should have the default one, as i don't recall ever changing it or modifying anything about it, but I could check if some kind soul can tell me how.
The problem happens quicker and more frequently when the tablet is put to stress (for example, when i'm flashing something or when a Gapp is updating/intalling).
I thank you in advance