Rainbow colors when hardly pressed the screen. topic

I popped of my tab's back cover to remove the battery so it will be calibrated, I did it before and it was succesful, I tried to do it again , then I noticed, a rainbow effect or whatever it is shows when I hardly touch the screen. I don't know what seems to be the problem, I didnt touch the lcd or other things but the battery and its connector/cable. Any help?