Power light turns on but turns off

A broken 2DS that I bought off eBay can be turned on, although the screen never turns on and the power light immediately starts fading out (As if the 2DS is powering down as normal). I've tried reseating the ribbon cables, but that has not helped.

I should also mention that this specific system is the PWB/CPU/AU-C/FTR-20 revised board (FTR001N, as the back cover states).

The system does not have an SD card inside, and I’ve tried adding one, but that doesn’t help. I’ve also tried booting it up with the button combo that bypasses the 3DS menu (Sleep+X+Start+Select) but that didn’t help either, it just did the same fade on, fade off.

What might be causing the problem? There’s no visible water damage, either.