VGA analogue signals need the Clock and Phase settings adjusting correctly via the config menu/OSD.
First make sure a "busy" image is displayed - something with plenty of fine detail such as a spreadsheet or document containing small text.
Now adjust the Clock setting so that the interference is even across the screen (you will see vertical bands of interference, adjust Clock until all the bands disappear, always choose an even number, odd numbers are almost always incorrect). Now adjust Phase for the sharpest and most stable image.
You can use the Auto Adjust / Auto Setup feature to automatically set Clock and Phase if you prefer, although you may get slightly better results fine-tuning these settings manually.