Can I use dell inspiron 3043 all in one PC monitor(has a HDMI IN) as an output device for MacMini?

- Only if the Dell has an HDMI INPUT. In that case you will also have to use the Dell normally with the Mac's screen being a window in a suitable app.

- You can also do it over the network with an app like:

ScreenRecycler

- Decent monitors are cheap and I would just get a new or used monitor.

how it works depend on the all in one

it could be that the hdmi will not auto display it's input on the screen

unless the all in one is running and some dell program which display the hdmi source is maximised