Question GPU causing PC to not boot?

[ReemiReemo]

Hey everyone I woke up today to find that my PC would turn on for a split second then turn off, after dismantling it and unplugging everything none essential I find that the PC won't boot at all if the GPU cables are plugged into my GPU.

If the GPU is slotted into the PCIE but not the motherboard it also boots up but not if it's plugged in and since my CPU doesn't have an IGPU I can't test that either.

I've tried:
Reseatting everything including GPU
Plugged ram one at a time
Reset my the CMOS battery on my MOBO
Tried different VGA cables from my PSU

I'm not ruling out the PSU being the issue yet until I can borrow a friend's GPU but I just wanted to ask if a faulty GPU possibly one that short circuited for whatever reason could cause this or perhaps someone could suggest another possible component that may be causing this, Thanks!

PARTS:
RX 6600
R5 2600
B450M STEEL LEGEND
SEASONIC SIII

 

[Lutfij]

perhaps someone could suggest another possible component that may be causing this, Thanks!
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SEASONIC SIII
How old is this PSU? What sort of a wattage does the unit have? Try and source(borrow, not buy) a reliably built 650W PSU and see if the problem persists.

 

[ReemiReemo]

perhaps someone could suggest another possible component that may be causing this, Thanks!
+
SEASONIC SIII
How old is this PSU? What sort of a wattage does the unit have? Try and source(borrow, not buy) a reliably built 650W PSU and see if the problem persists.

I've had the PSU since about September 2020 it's 650watts, not sure if I'll be able to borrow a PSU but I'll try my best to.