Not Detecting Second Monitor. Looking up "can't detect second monitor brings me to a bunch of results saying to check in Activities -> Settings -> Displays. Having a second monitor connected to your computer is like having additional workspace and useful when there is a need to monitor spreadsheets and have both visible simultaneously.
In this guide, you'll learn the steps to troubleshoot and resolve common issues with external displays. Computers are commonly unable to detect the second monitor due to faulty, outdated, or corrupted video drivers. When I go to Settings > Display, only my primary monitor is detected.
EDIT: I've noticed only my bottom DVI port is working properly on my card.
These may resolve your issue with the second monitor not detected before you need to dig deeper into other issues.
Now, tap on display from the available list. Second Windows or Mac monitor not working? Both are asus monitors and I can get either monitor to work It does not show a second monitor being detected at all.