if you think you can do this right then try it, but do it at your own risk. I fixed mine using this method and it works great. So the top screen has 2 flex cables that make the screen work. My guess is they're probably loose. Here's my way to fix it. Unscrew the 4 screws on the bottom of the system and remove the back plate, sd card, game card, and battery. Then unscrew the 9 screws on the plastic and (VERY CAREFULLY) remove that plastic. Try not to strip the screws, as you'll need them later. find the flex cables connecting the motherboard and top screen. re-connect them to the motherboard. Put the whole thing back together and then you're done!
The_Renegade_Arceus
www.youtube.com/user/RenegadeArceus