Nintendo DSi repair - is the top screen the problem?

So I’ve been attempting to fix this DSi for a good while now. Turn it on, blue light appears, bottom screen flashes momentarily and then the DS turns off. I’ve replaced the top screen with what I thought was a good screen, bought it especially as a replacement. It was working at one point, but then I attempted to rehouse the guts and when it was all back together, it started doing this. I’ve clearly buggered something but I’m not entirely sure if it’s the top screen. Obviously, there’s a chance that the top screen replacement I bought is buggered too, but I’d like to make sure that it’s not some other fault before I order another one.

Does anyone know of any other fault in the system that could cause the bottom screen to flash on for a moment like this? Or is it most certainly a top screen fault?