Mac Pro 2013 is not powering on (lights On , Fan Off , No Chime )

Hi, to make this short as possible

Note I also posted is also on another site and I’m gonna include everything with yesterday’s updates at the end.

I replaced the GPU on my Mac Pro 2013 and while doing that I replaced the thermal paste for the CPU too now the computer is not powering on ( No POST ) I have the lights on except the power button light is off .. first I thought it's something with the new refurbished GPU but it's not because I tested it with another working GPU.

• The battery inside needs a replacement ( I did a replacement with no luck. )
• The power supply is not working ( I can see the red light after hocking up the power cable ( Without the logic board installed if the logic board is connected to the riser the red lights in the logic board and the PSU will go off as normal behavior ) I also get the green light when I press the little check button on the I/O board from the inside ( more details about this at the end ) then I used the multimeter to measure the power that it's going to the CPU riser and it's giving me 1V .. I don't know if it's the right number.
• The logic board got damaged? but why? everything is fine also it's red light is on when it's connected to the PSU only .. it's not my first time disassembling the Trash Can and I did it so many times and I even looked at the sensitive data cables that connect the logic board to everything I can't see any broken pins.
• Someone said press shift on the keyboard while turning on the device but I’m using a USB keyboard and there is no power on the USB ports ! the screen wakes up though pressing the power button (connected via thunderbolt )

Finally, I always take precautions like wearing an anti-static bracelet and not using any screwdrivers with magnets also changed the power cable connected it directly to the wall

Please help .. Thanks

TL,DR : I/O lights On except the power button No Chime No Fan Just the Lights for 15 sec then they go off .. PSU seems fine ( I might be wrong ) .. I put the older GPU back, replaced the battery with no luck.

UPDATE #1 :

I followed this guide ++https://logi.wiki/index.php/Mac_Pro_6,1_...

I got #2 & #5 on while the computer is off .. will try to do power on without the lid I just need a magnet that I don't think that I actually have at the moment

UPDATE #2: I managed to find a magnet and activate the computer power without the cover being on ( if you wanna do it too just stick the magnet next to the power button outside the seam. )

Now thankfully I got all the Diagnostic LEDs on Green Light Except the first one which means everything is working !!!!! then why it's not POSTING !!!!?????

Also, does anyone knows how to check the CPU Riser LEDs without dismantling the whole thing and make everything dangling with a magnet stuck to the I/O it’s seems a little bit dangerous to do that?

UPDATE 3 : I just noticed that Error LEDs ( two RED ) on the logic board are on ! ... Still don't know what that supposed to mean.

Please help

Thank you