Sometimes VGA and HDMI cables conflict - have you tried DVI and HDMI?
Have you tried to uninstall driver and reinstall it while monitor was attached by HDMI?
Are your monitor drivers up to date?
Have you tried this?
1) Uninstall the driver if it's already installed. Then when you install/reinstall it instead of double clicking on the install file right click it and select "Troubleshoot Compatibility" 2) Then click "Try Recommended Settings" and in the next windows click "Start the Program" to install it. 3) After it installs see if it works correctly
Is your second monitor recognised by the Windows Display - control panel, appearange, display, connect to an external display?