All in one desktop as second monitor

24-5488 spec:

Use the HDMI-in port (#3) so you can use pc as display monitor only. 

Yes HDMI in can be used for using it as extra monitor. 

Internal Speakers won't work though,  

This is the last thing I needed to do.  Worked after i shut off the monitor.

Pay attention to 2 things:

- one of the HDMI ports has an extra icon that shows it's an input
- at the bottom of the screen there is a very small button left of the power button

1) Just plug in your HDMI cable coming from your laptop into the HDMI input
2) press the small button on the AIO, it will display HDMI on the screen
3) on your laptop you should be able to press WIN-P to connect to an external monitor (or there's a function key with a rectangle displayed)

You can toggle back and forth between using AIO as monitor or computer just pressing the small button.

Back of screen, notice the HDMI with an extra icon showing it's an input

Bottom of screen - little button left of the power button

Using the little button on the AOI to switch between the PC display and acting as an external monitor for a 2nd PC works well when running Windows. I also run Linux on this PC, and when running Linux the little button doesn't work. I don't know if this is a driver problem, a Linux problem, or Operator Error problem. Any help/insight would be appreciated (Model is an Inspiron 5400 series AIO)

@mpl55378  - Dell doesn't support Linux on this model so I'd suspect it's a software issue.

Changing the input source is controlled by the Dell On-Screen Display Application, which isn't available for Linux...