About a week ago I went to build my new PC stuff and when I went to turn the PC on everything powered on but the graphics card. At first I thought it was dead but then I noticed when I went to mount the motherboard that the metal plate on the left side that connects the PCB to the cooler was preventing the card from being fully pushed in. I'm assuming this is the issue because when I took my PC out of the case to test it with it without the back of the case being in the way, everything worked perfectly. (and when I went to put it back in the case the same as before happened, everything powered on but the graphics card and there was no display)
I would take a look at how the mounting of the motherboard is. You may have misaligned your motherboard so that your expansion slots don't have as much room to be secured.
There's only one way to mount the motherboard so can you please explain what you mean more? There's only one option for the motherboard screw holes and it aligns perfectly with the back case slots it's just the graphics card can't be pushed all the way in on the left side. The only solution I can make sense with is that the motherboard is pushed in too far but I don't understand how that is a building process error as all I made sure I put the screws in loosely.
Sometimes when you screw things in you do it in such a way that it can push against the expansion slots which means its not perfectly screwed in. I'm saying just because it's screwed in and mounted doesn't mean its perfectly aligned.