I have Dell Optiplex 3020 desktop. I have dual screen setting. Main screen is connected to HDMI and second smaller monitor is connected to VGA. System don't see all resolutions available for VGA (only up to 1024x768). I know how to fix that- i put in console: xrandr --newmode "1440x900_60.00" 106.50 1440 1528 1672 1904 900 903 909 934 -hsync +vsync and then: xrandr --addmode VGA-1 1440x900_60.00
Then I configure everything in settings. Everything seems to work ok. I restart PC- GRUB by default is displayed on my HDMI screen, splash screen too. After I give my password screen (HDMI) goes off and I see only things on screen VGA in resolution 1024x768, all changes done by me seems to be forgotten by system.