I'm facing that problem since last weekend. Yesterday i made a full reflash but w/o many hopes and like i was figured out, nothing changes. Now i'm pretty sure that its a hardware problem. Today i've got my device opened and nothing seems to be wrong. All flex cables properlly connected and nothing seems to be broken, wet or something like that.
So, what do you guys think about this flickering horizontal lines problem ? How can i try to fix that ? For now, i have 2 choices: either buy a new flex cable http://www.parts4repair.com/nokia-n9...-front-camera/ or buy a new display http://www.ebay.com/itm/New-OEM-Noki...-/120746249398. What do you think that could be a better choice ? I just don't want to waste money That kind of sttuff are pretty expensive here in Brazil.
I really need an expert opinion here ! Thank you very much.

Edit: after buying and install a new LCD, the problem still there. So, i did order a new ribbon and now it works. Just for record, it's sooo easy to change that ribbon. I just recomend that you use the right screwdivers. No place for workarounds here or you will fuc* your screws.
Thanks all.