Rusting parts

Hi guys

I was trying to revive an old pc and when I open it up I realized wow. Theres rust on some screws and now I see there's rust on the GPU and some green stuff that looks like mold.

So was wondering, even if I cleaned it. Should I try and plug a new psu in to see if it starts up?

Worried about the part the the screw rusted on the corner of the PCB of the gpu

And some dust on the heatsink

My old PSU is rusted out with the vents so I don't want to risk using that. Motherboard seems clean and fine, interlooped water-cooled do the cpu is fine with the radiator.