Lines and trembling in Acer laptop screen

During November a group of horizontal lines and a curious graphical effect of repetition suddenly appeared in my Windows task bar. This was just a bit annoying and I continued using my computer, also because this problem did not show up in screenshots, so I could continue working as usual.

Around two months ago the pattern of horizontal lines in my task bar changed a bit and I did not care at all. But some days ago something new happened; one or two flickering lines appeared near to the top of the screen and the image trembled, jumping up and down one or two millimeters. This problem appeared two or three times and only during a little time, and then it disappeared for quite a long time.

Today the problem has suddenly become very bad. Another group of lines has appeared in the task bar and the image has moved up above the lines, so the task bar is now about 12 millimeters from the bottom of the screen and the image is often trembling. Also, the image is cut where the upper flickering lines are, whereas the narrow strip of image above these lines is always static and correctly positioned. Because of this problem I can not see the address bar in an explorer/browser window nor the Back and Forth buttons…

What I find more puzzling is that if the image is not trembling it will start trembling if I open an internet browser or a Windows Explorer window; then it will stop trembling after I close these windows. Usually the image does not tremble when only the desktop is showing up. However, while I was writing this letter and the desktop was showing up, the image began to tremble; but, right when the desktop automatically changed its wallpaper the

I have visited the BIOS and the problem still existed there. I have connected an external monitor and the problem was not present there. I have opened my computer and moved the screen cables to see if something changed, but nothing happened. I do not expect to be able to solve this problem but I would like to know what exactly causes it.

Thank you in advance.