lvds vga
DDC lines need to go to yor VGA controller, and (normally) tell your computer which monitor is connected and which resolutions are supported.
Use a short cable when trying, longer cables might fail communication.
Try some different VGA resolutions, especially the lower ones.
Try to startup your PC with the board connected, maybe your PC only looks during startup.
Also, if your computer is already connected on DVI, VGA output may be disabled.
Start your computer on VGA cable monitor.
Hopefully it helps.