It would help if you posted the brand and exact model.
It would help if you posted the brand and exact model.All-in--One desktop
And exactly what version of Windows (or other operating system) is running the computer.It would help if you posted the brand and exact model.
Is the screen completely black with a line across it or is the line over a full screen of video?I notice that there is one horizontal line across my screen.
I don't think you mean that. An AIO is like a laptop and has a graphics chip soldered to the motherboard. You probably reinstalled a driver.I have already reinstall my graphic cards
The Aspire C27-1655 mentioned in post #4, does have an HDMI output according to the specs on the Acer website. Mirroring the built-in screen to the external monitor should work as a quick check.It would be nice if the computer came with a way to plug in a 2nd monitor but most AIO don't have any way to do this.