If the lines are appearing and disappearing then it is not dead pixels you are dealing with but it could still be related to pressure.
If you are careful you can troubleshoot the problem yourself. You will have to work with the back panel removed leaving boards exposed that contain very high voltages.
With the back panel removed at the top of the casing you will see a long circuit board (Usually about the length of the screen) There will be a number of ribbon cables plugged into it, coming from the front of the casing, the cables power different sections of your LCD screen.
Now with the TV propped up power it on and play something as you normally would, find the ribbon cable at the top that is closest to the lines on the screen, carefully you should be able to move the cable a little, see if the screen corrects itself.
If so, plug the TV out and press the power button a couple of times to discharge any remaining power.
Now lift the tab for the cable you identified and push it in fully and clip the tab back down on it, turn on the TV and see how the picture looks, if it is good then close the machine back up and enjoy some TV.