Not sure if you are still having this problem, but I was able to solve the issue on Windows 10 with mine. Access your BIOS menus on startup. This is typically done by pressing Function Key, also...

Thank you for the suggestion on this. While I didn't need to clear the CMOS, I did boot the BIOS menu during startup, and found dual monitors was not [Enabled] in the settings. I have zero idea how...

Machine: Lenovo - Ideacentre 300S Desktop - Intel Core i3 - 4GB Memory - 500GB Hard Drive
OS: Windows 10
Processor Model: Intel 4th Generation Core i3
Graphics Card: Intel HD Graphics 4400
...

I'm actually experiencing the same problem. I bought a Lenovo Ideacentre 300s 8L and got it up and running. Everything was working properly for a while and I had no problems. Recently I unplugged...