How to Troubleshoot Multiple Monitors Not Working

1. Test the monitors on another computer. Make sure both monitors are in working condition.
2. Plug one of the monitors back in to your main computer. Use the monitor connection port on the back of your computer that corresponds to your two-headed video adapter. Don’t plug the monitor in to the blue onboard video plug that is built in to your motherboard. This onboard port is usually located near your mouse and keyboard ports.
3. Turn on your computer.
4. Note the status light on this monitor when you boot up the computer. If the status light doesn’t come on at all, the dual video card is sending no signal to the monitor. If the status light comes on green or blue, but then turns yellow or amber, the video card has a problem.
5. Switch the monitor to the onboard monitor port and reboot the machine again. If the monitor status light does not come on at all, or if the “green then amber” signal is observed, you have an issue that requires further testing.
6. Leave the monitor plugged in to the onboard port. Reboot the computer and enter the BIOS setup by pressing 'F1,' 'F2' or 'Delete.' Navigate to the video properties section. If you find a command line that appears to switch your computer between the onboard video adapter and your dual video adapter card, turn off or disable the dual video card or enable the onboard card. Press 'F10' to save this change and reboot. Make sure the monitor is now plugged in to the onboard video port.
7. Observe the results. If the status light does not come on, or if it switches from green to amber again, your motherboard has probably been damaged. Seek professional help.
8. Continue troubleshooting if the monitor works on the onboard video adapter port now. Use this connection so that you can “see” to fix the dual video adapter.
9. Go to “Start,” “Control Panel,” “System,” and “Device Manager.” Look under the “Display” listing for your dual video adapter. If the adapter listing has a yellow caution sign or a red X through it, the driver has been disabled or is bad. If you turned this dual adapter off during the BIOS tweaking in a previous step, reenable it now using this Device Manager panel. If your monitor goes blank, switch the connection from the onboard video port to the dual video port. You should see an image now.
10. Download and restore any drivers for this device and reboot your computer if nothing changed after you enabled the dual video port. Switch the monitor back to the dual video adapter as you reboot. If no image comes up on the monitor, switch the connection back to the onboard port so you can “see” again.
11. Go to “Start,” “Control Panel,” “Display” and “Settings.” You should see the dual video adapter listed. Enable this device in this screen and switch the monitor cable back to the duel video port. If no image appears, switch the cable back to the onboard port. Reboot.
12. Switch the cable back to the dual video adapter port if you get no monitor image this time. The dual video adapter port should theoretically work now if the onboard port is no longer functioning.
13. Re-run all these steps using the other video monitor just in case the first monitor is configured incorrectly.
14. Check the monitor refresh rate next, using a monitor that works in one of the two video ports. Refresh rate settings are found under “Display,” “Settings,” “Advanced” and “Monitor.” If the refresh rate is set at “60 mhz,” for example, and the nonoperating monitor is configured at a rate higher than 60 mhz, this could be the solution to the problem.
15. Configure the troubled monitor using the monitor’s own configuration onboard panel. A menu button on the monitor near the power switch will usually bring up this panel: the monitor does not have to be plugged into the computer to use this tool. Configure the monitor to run at the proper refresh rate. Plug both monitors into the dual video adapter and observe the results.
16. Consider replacing the dual monitor video card if your troubleshooting has produced no positive result regardless of which monitor you use for these diagnostic tests.