Do not run this monitor like so, you will cause burn in on the center of the screen and it can happen very quickly.

This can be several things, bad solder, bad capacitor or damage to the frame amplifier. What tools do you have ?

I did actually open it and fully disassembled the boards. I couldn't find anything visually outstanding. All caps look good, no burnt nor chipped components. The monitor's VGA connector soldwr joints were actually broken. But that's a different issue, which I fixed already. Now you see the picture coming from the PC, but the squishing is unrelated to this fix. I feel there's something in the vertical trace circuit, but I don't know how to identify that circuit let alone find the faulty component.

Cheers!

Photos of the inside can be helpful then and even better is an actual schematic if it is available for it, which will greatly simplify the process ~