This has just started happening lately...I'm on my pc and suddenly it will change size - from fullsize to a smaller curved screen. Is there a way to fix this problem? Even though I can adjust it from the monitor control, it is only a temporary fix as it will revert to a curved screen at random times..also happens sometimes whenever I start up.
This is a great community. Thanks to all techies for their help in the forums.

This sounds like a problem with a loose or bad connection.
Check the monitor cable to be sure it's tightly connected. Look for bent or damaged pins.

My monitor has a
degaussing feature, that I believe demagnetizes the electronics within the monitor that have built up static charge after time. Look at your monitor options using the buttons on the monitor, and there should be the degaussing option there. Try that maybe?