Most modern computers can do dual display.
However, if one monitor is looking bad it would likely be the monitor or the cable.
I have a older Dell desktop with Winnows 10 and the main screen is a TV set that allows VGA input. The other is from a GPU card that drives a HDMI cable .
There are many, many variations you could have.
If you provide some details about the computer, some expert here might be able to help. Please mention what OS you are using. Is it Windows 10?