Plug In 4 Pin And All Other Power Fails. Why?

Which graphics card ?

Your power supply must have at least the minimum capacity required to support a system with the graphics card you are using installed, or the max graphics card you might install in the future.
(Onboard video – video built into the mboard – IS NOT A CARD ! )
If that info is not in the ad for the video card, you can go to the video card maker’s web site and look up the specs for the model – often under system requirements – the minimum PS wattage, and, more important, the minimum amperage the PS must supply at 12v is stated. If you don’t find that, any card with the same video chipset including any letters after the model number has very similar minimum PS requirements. Some power supplies have two or more +12v ratings – in that case, add those ratings to determine the total +12v current capacity.

If you’re a gamer…
In most if not all cases, the max capacity rating of the PS is an intermittent rating. It’s recommended that you do not load your PS to any more that 80% of that rating if you are going to be using something that puts a constant load on it, such as playing a recent game for hours on end. In that case, you multiply the min capacity stated for the system with the particular video chipset on the card by 1.25 to find the min. capacity of the PS you should have.

“Power Supply: XFX: XXX Edition – XPS-650W-3XS”

That may not have enough capacity, depending on which video chipset is on the video card, or it may have been defective.

Power supplies that don’t have enough capacity for when the video chipset on the card is installed often work fine when you first install the card, but the power supply is being overloaded and it WILL be damaged, sooner or later.

” I have recently attempted to power only mobo and CPU with 400W and still nothing.”

If the video chipset on the card requires a minimum of a lot more than 400 watts, the computer probably will not boot when the card is installed.

Try your “XFX: XXX Edition – XPS-650W-3XS” with the computer you got the 400 watt power supply from, or with whatever working computer. If it doesn’t work with that computer, either you have damaged it or it’s defective.

E.g.
My brother had a high quality Antec model that had a defective controller chip. If you placed a small additional load on the power supply, in his case when he tried to burn a CD, it black screened and rebooted the computer.
I have an old K6-III 400 system that also has a defective controller chip – it’s average quality power supply shuts off the mboard when you plug an external drive into a USB port (it draws 500ma @ +5v – 2.5 watts) !