Mac Pro 2013 is not powering on and GFXB Check lights on

Hello everyone

I have an mac pro late 2013 which i bought it from someone as defective.
He sad one morning it stop working and Apple could not find the issue.

I have started troubleshooting and came across to this point where GFXB Check lights on on the bottom logic-board. When i read the Manuel it says that, :
”GFXB Check: This indicates that there is a connection issue between the logic board and Graphics Board B. Check the mezzanine connectors on both the logic board and graphics board to be sure the connections are fully seated.”

I already checked the connections where two pins were bent (I think this guy has tried to fix him self and bent it while assembling back)I swap the cable from Board B to Board A but it still on, that means its maybe not the cable.

My question is, can it be something else if yes what should i go after.
I have the lights on except the power button light is off.

I have 5 Diagnostic LEDs on io/board
Thank you.