PS4 Pro won't boot. BLOD.

I'm trying to fix an old ps4 pro for my friend. Whenever i try to switch on the device I get a single beep and a blue light which turns off after a second. No display on my tv. Pressing it again after a few seconds gives the same result. If I press the eject button I get 3 beeps. Opened and cleaned it. Still won't work. Ordered OEM psu and replaced it. Still the same issue. I'm out of ideas. Does anyone know how to fix this? Thanks in advance.