Recently my iMac had been experiencing problems, I took apart and checked everything and put back together. Problems were gone but the screen suddenly started gradienting from brighter on the top to darker on the bottom. Brightness overall is also lower now. My question is what can be creating this? The black tape that was around was ripped, I've heard it's creating static isolation, can that be it? Also I possibly pulled power cord too hard, can it be possible that display is not getting enough power? I appreciate any theory or advice. Thank you.