Hey, the DS Lite code of faults is.
Bottom screen flashes on then off = top screen fault.
Top screen flashes on then off = bottom screen fault.
Sometimes when you order new parts - a defective one could arrive, so if you still have the old bottom screen - try it on it.
Or check the ribbon is connected properly, it should be in a straight line.
Worst case scenario the connector could be damaged, (sometimes this can be caused by the DS getting wet, but i've also had a couple that had dodgy connectors without the console ever being wet)
So theoretically speaking if my bottom screen flashes, I can rip off the top screen to make it a GBA and it will work?