PS4 Blue light of death, what is the cause?

Hi there, i’m reaching you because i would like to know what is causing my PS4 to have a BLOD,

I got my PS4 used, already with a BLOD, i tried to fix it by using the washers technique, and after a bit of trial and error, it worked, but with a catch, and that’s why i’m reaching you,

I cannot boot my PS4 the usual way, (at least a very very few times, if not at all).

To manage garanteed success in booting the console i must boot it directly into factory mode, then choose “restart PS4” for it to propely go into the OS of the console.

If i don’t do this, when i boot the console i get pulsing blue light endlessly. I get fanspin and HDD Spin tho.

To power off the console in this state i must maintain my finger on the power button until i head a beep and the powersupply switching off.

EDIT : Just to try, i tried to go into the safe mode, and now, constantly when i press and hold the power button until i hear a 2nd beep, it beeps but shut itself off right after that….

Do you guys have any suggestions, maybe @tronicsfix ?