ds lite bottem screen flash no boot

Sorry for the late reply. I'm just starting to look over unanswered questions, but I think I can help here! When the bottom screen flashes like that, it means the connection to the top screen is broken. The system detects a break in the circuit and powers down. You'll need to replace the top screen with a working one. There are a couple guides on here that can help walk you through it. This one is good, but I've found steps 23 and 28 to be unnecessary.

For the black cable, if you mean that it is routed under the game card slot before connecting to the WiFi board, that is normal. If you were working with the system and the connector is now caught under the card slot, then the only advice I can offer is to gently work the connector back to the side with the WiFi board and pull it back out with a thin set of tweezers. Once it is back out, carefully try routing it through again, keeping it close to the outer edge of the DS, as there are fewer obstacles there in my experience.

Hopefully that was helpful!