I would like to take a moment and thank you for using this forum, it is a great place to find answers.
I understand 2 of your HDMI ports aren't working,
No worries as I'd love to help, however, I need a few more details to provide an accurate solution:
You are attempting to set up a dual display, is that right?
Did you ensure your computer/graphics card supports dual display?
Have you checked your user guide for details about the same?
Also does the HDMI port work with one monitor at a time, one each? if it doesn't, please follow the below steps:
Use the correct HDMI cable for your HDMI device
Most HDTV devices have more than one HDMI input port, therefore it is very important that the HDMI display's input source is set to the same HDMI port that is connected to your computer, for example HDMI 2 to HDMI 2.
Select HDMI sound output as the default audio device
Windows outputs sound to only one device at a time. Select the desired output device by setting the default device. The sound then changes to the correct devices as cables are connected or disconnected. When switching between the sound on the computer and the sound on an external monitor or TV, open the sound devices to ensure the correct output device is selected.
If the device has not already been configured, the HDMI output does not display in the sound properties unless an HDMI cable is connected between an HDMI device and the HDMI port on the computer.
Use the steps below to configure the audio output when an HDMI cable is connected. This will allow you to select HDMI as the default when you are using an HDMI connection. When you are not using an HDMI connection, the sound settings default to your computer's speakers and headphones.
Connect the HDMI cable to your computer and to your output device.
Right-click the Volume icon on the taskbar.
Click Playback Devices.
The Sound window opens.
On the Playback tab, select Speakers and Headphones, and then click Set Default.