Part of top screen reflecting in bottom part of screen (just an image popping up but very annoying!! ) Please help me!

Hi. I have a problem with my laptop(Dell Inspiron 1420) screen. Part of the top screen (approximately the full size of a windows vista/7 taskbar) seems reflecting in the bottom part and well, it doesn't affect my taskbar or anything that is in the bottom part when i'm on desktop or running a program or game. I've recently installed windows 7 on the laptop but i don't think that is the problem as this problem was occurring even when i was using the windows xp pro sp3 before. This problem started to occur yesterday and I usually turn off the laptop before going to sleep and this morning when i turned it on, i was surprised that this problem was not here anymore but unfortunately it was only for a few mins after which that problem started to occur. I even noticed a horizontal green line closely above a horizontal red line(its position is a little below the upper horizontal line of the taskbar) in a black background(noticeable when pc is turned on, windows is loading...)

From my point of view, it is not a problem with the OS or any software, it is a hardware problem maybe heat?? (as just when i turned on the pc, this problem was not there but appeared after a few mins)..Please help me, that thing popping up about 2 sec is very annoying!!