I would have checked the Event Viewer, System and Application logs - to see if I had found any warning or errors realted to graphics, drivers or monitor.
Next, possible using the driver sweeper - uninstall the drivers - used the driver sweeper and reinstalled the drivers just to see if it made any difference.
Third, I might have check if it was enough power o the PSU (watts) to run the adapters.
Hm, thats about what I can think of ...