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.