Top screen not working

I’ve just started on my first Nintendo 3DS repair I managed to get it to a position where it turns on but the top screen remains blank. This is the tricky part to explain. Although the top screen doesn’t turn display anything it’s not entirely blank. The screen colour changed from black, to a black with a blue hue. It’s clearly giving off light but nothings on the screen. The bottom screen however is perfect.

Does anyone know what the problem might be?