New 3DS XL won't boot, has popping noise

First off, thank you for responding. Second, that time I said all I had to do to get the system to work was plug in the ribbon cable for the top screen into the motherboard the right way, before I did that, the system at least booted into the bottom screen and I could even see the backlight on the top screen as well. I remember, even when the ribbon cables for the volume and 3D had a chunk missing from the connector, the system would still boot. All I did after fixing the system and putting it back together was take apart the bottom half one more time and replace the home button cable with a new one I got off eBay. After that, it stopped working again. Are you saying that my problem could be the cable for the home button is a faulty one?

It could be a faulty cable, or just the wrong cable. When buying parts for this device, I find a lot of the vendors are just selling parts and do not know the difference between something like "new Nintendo 3DS XL Home Button" (lower case new, as in a new part that has never been used) and "New Nintendo 3DS XL Home Button (upper case New, as in for the device with New in the marketed name). Because of this confusion, many parts are listed incorrectly, even on some websites that are dedicated to Nintendo consoles.

This is partly Nintendo's fault for having such a bonkers naming convention, but also vendors should be more careful to be accurate with their item descriptions.

But yes, if you did have it working before trying to replace the home button cable, Okkam's Razor suggests check there first. Try again after putting it all back together, and if that doesn't work try again with the original part. If it works with the original part and not the new/New one, I think that suggests the culprit.

Ok, so I just tried replacing the ribbon cable for the home button with the original one that came with my system and I still get the pop sound. I really don't know what else could be causing the problem. I will admit, I saw a very small tear in the speaker cable on the part that connects to the motherboard, but I remember even with the previous speaker cable I had, it was brand new, had no tears in it at all, and still the same result. What else can I try? Please let me know if there's anything else.

An additional cable to check that many people overlook is the cable (well... 2 cables) that connect between the upper screen and 3D switch board. Those two little short cables are capable of being the culprit if not plugged correctly, and it is something that is often overlooked since they're not part of or connected to the motherboard.

Yes, a tiny tear in that speaker ribbon could also cause this. Perhaps a coincidental timing. I don't know, but I would recommend trying to change that out if the other one without the tear is available.

If all else fails... well, it probably is a motherboard fault and if you're not down with diagnosing and microsoldering if you are able to find the exact fault, replacing the motherboard is your only option, sorry.

I actually bought a replacement motherboard, that was used, from eBay, but it was taken from a working system. And I still got the same result. How would I go about checking faults in a motherboard? I checked the fuses on the motherboard with a multimeter, and they were both fine. And from the pictures I sent you, specifically the one with those two ribbon cables you were talking about, do those cables look like they were plugged in right?