My laptop is Core i5-2410m when plugged into an HD monitor when I want to play a game and select this resolution it always says not supported...why?
When an OEM builds a system they can limit the resolutions that will be available in the computer, which is done at video BIOS level. You can check the specifications of the HD monitor to see if it supports that resolution or not. As a recommendation you can try updating the BIOS and drivers of the laptop. If issue persists after that you can contact the manufacturer of the laptop to see if they have tested that resolution in that laptop.