Alienware Aurora R4 Not Booting, Power Button Doesn't Work

My system: Alienware Aurora R4, i7-3820 CPU, 2 x Nvidia GeForce GTX 660 GPU in SLI, 8gb RAM, 1TB HDD, 24" Dell U2410 monitor.

I'm posting this here just in case anybody else has a similar problem. I've been working on this on and off for about 28 hours, which was when I got my computer in the mail.

Problem: after assembly, the power button on the desktop didn't work.

What I tried: I verified the outlet was working, the power bar was functioning properly, tried different outlets, different power bars, and no power bars. I tried switching the power cord with the one that came with my monitor (Dell U2410 24"). I opened the chassis and verified that all the required plugs were secure. I unplugged and replugged all of them. I reset the CMOS by removing the top GPU (Nvidia GeForce GTX 660 OEM 1.5GB) and moving the second CMOS jumper from the 2-3 pin to the 1-2 pin. I tried unplugging the power cord from the computer, at the insistence of the tech support representative I ended up speaking with, and holding down the power button for two minutes, even though the power button didn't actually work.

The only thing that managed to turn the computer on was holding down the power diagnostic button (the small black button on the power supply right beside where the power cord plugs into). The only problem was, as soon as I let go of the button, the spring pushed it back out and the computer would shut off again. I'm ashamed to admit that, after tech support told me that my computer was DOA and would have to be returned, serviced, or replaced (as I was still within my 21 day return time period as well as the warranty), I tried a workaround. I wedged something between the computer tower and the wall in such a way as to keep the power diagnostic button held down. This let me use the computer. I figured, since it was a Friday night, I'd use it like this for the weekend and then, some time during the work week, have a tech come over and replace the power button assembly (which I had assumed was the problem, since it was the only part of the computer's interior I couldn't physically get to). A quick check inside the chassis, near the front and just behind the bottom of the front bezel, showed that the amber power indicator light was on, which told me that the device was receiving power, and my being able to use the power diagnostic button at all confirmed it.

An hour ago, I gave up on the workaround I'd established. The slightest movement of the desk would turn the computer off. Not good when you're busy gaming.

What ended up working: on the regular Alienware Aurora chassis, as well as the Alienware Aurora ALX chassis, the very back louvre/panel lifts up at the back and releases the mechanism that holds the left side panel onto the chassis, which grants you access to the computer's interior (motherboard, hard drives, optical drives, etc). When the side panel is replaced, it clicks, but the back louvre/panel does NOT go all the way back down. As long as it is up, it appears that there is some kind of built-in switch that prevents the computer from powering on (unless you're pressing the power diagnostic tool for troubleshooting purposes). Make sure this panel is pressed all the way down until it is flush with the rest of the top of the chassis. There will be a click when it makes it, but you shouldn't have to force it.

I was very close to returning the whole works and buying my computer from some other company.

A few problems I have:

1) The rear louvre/panel was not pressed all the way down when I opened the box that the computer came in. This is what would cause the above problem, and I shudder to think of how many people might have returned their desktops for the same reason I experienced.

2) Where the dual graphics cards' plugs stick out of the back of the chassis (the DVI/DisplayPort/HDMI plugs), one of these sections is covered by a black plastic piece, preventing the end user from plugging the monitor into the wrong graphics card. My computer had the second (lower) GPU's plugs covered. When in SLI, the second (lower) graphics card functions as the primary video source. Plug your monitor into this one, not the first one (unless you're using more than one monitor).

Had I been less determined and less experienced with computers, if I were just your average user buying a nice computer to play games on, either one of these problems would have resulted in me mistakenly believing the computer to be defective in some way. In fact, one of them did, and I nearly returned the computer and monitor entirely.

I hope this can help some of you, as all of my Googling provided no results for my own problem.