"Not recommended" problem

Jun 20, 2018
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iam using a pc monitor of 1440×900 recommended resolution .
i tried to connect hdmi to vga using set up box in order to watch tv on my monitor .
the problem is that , at the very few seconds its working but with an alert prompt of , Not optimum mode : Recommended mode 1440×900 60Hz although the resolution set is the same and after some time the video goes and black screen comes where the alert message prompt is moving .
i got only four resolution modes in my set up box , they are 1080p , 1080i , 720p and 576p .
how can i solve this problem ??