This has been resolved. Thank you  
I am working on a Dell all-in-one trying to get the display working again. I have power drained the pc a few times and to no avail will it show a display on the built-in screen. I have been able to perform the self-test with video button on the bottom side of the device. Please help as this is an urgent matter.
Dell All-In-One OptiPlex 5400 Display issues