3ds xl powers on but won't boot
Its 2 in the morning and I have been trying to repair a 3ds xl for hours. I am at my wits end here, so bear with me. I bought a broken 3ds xl off ebay thinking I could repair it. I do Ds lites all the time, and stupid me thought I could handle the complexities of a 3ds xl. First mistake. Second mistake was that i bought more than one. 3 (already broken) motherboards, 3 top screens, 1 stripped screw and various other swapping of parts later, I still don't have a fully functional 3ds xl. Here's my problem. When put completely together (minus a few screws for the sake of time), The 3ds powers on, the screens turn on (as in the backlight turns on) but the screens remain black. Things I've tried: Reseating all of the ribbon cables. Checking the wifi module to see if it's connected. Swapping the wifi module. Swapping the battery. Holding the power button down for 10 seconds while holding the wifi button simultaneously. I am already looking into buying a (functional) 3ds xl, so before you give me the Very Helpful (insert sarcasm here) suggestion of buying a new one (or a "New" 3ds xl), Please do me a favor and Don't.
TL;DR: I'm hungry, tired, and desperate. Please help me.
Edit: I forgot to mention that I have one more motherboard that I haven't yet tried. Should I try swapping that one out, or am I screwed?