That's function what I want to modify for fullscreen mode. I added this line Local Const $CDS_FULLSCREEN = 0x00000004 And replaced DllStructSetData($DEVMODE, 2, BitOR($DM_PELSWIDTH, $DM_PELSHEIGHT, $DM_BITSPERPEL, $DM_DISPLAYFREQUENCY), 5) with DllStructSetData($DEVMODE, 2, BitOR($DM_PELSWIDTH, $DM_PELSHEIGHT, $DM_BITSPERPEL, $DM_DISPLAYFREQUENCY,$CDS_FULLSCREEN), 5) But it still don't go fullscreen mode. I need to somehow pass $CDS_FULLSCREEN flag to ChangeDisplaySettings. By fulscreen I do