Check if your system is using discrete graphics instead of integrated graphics.
Currently using the HDMI port on the primary monitor, but when using the motherboard HDMI port for the 2nd monitor to use the integrated graphics the 2nd monitor is blank.
The video port on the motherboard only uses the integrated graphics which may be disabled when using discrete graphics which causes the blank screen. Most of the time a discrete graphics card disables the integrated graphics, this depends on the motherboard if it has a swithcable graphics feature. Contact your motherboard's manufacturer and check with them if it is possible to use both discrete and integrated graphics at the same time and how.
- Discrete graphics may also be called as GPU (graphics processing unit) or dedicated graphics.
- Integrated graphics may also be called as IGPU (integrated graphics processing unit).