Phenyx PTX-15 and Audacity

Hello Room,
I am a new user to Audacity so the question may sound dumb to many.
I set up a home studio as follows:
I am using Phenyx PTX-15 mixer. microphone is connected to it, so is the headphone. The record out is connected to computer and main out connected to the Audio Monitor. The main out is connected to the mic in of computer, Headphone out of the computer is connected to the audio monitor.
So this is the issue I am having:

  1. If I take out headphone out from computer to audio monitor( disconnect direct connection from computer to audio), when I play, I see all the sound bars are showing but no audio.
  2. If I connect the headphone out, I can hear the playback audio, however the headphone from mixer can not hear any of the playback audio, however in that headphone I can hear my voice when speaking on the phone.

In both cases, I have Microsoft sound mapper as mic and speaker input.
What am I doing wrong? why can not I hear the playback when singing?

Maybe my brain isn’t working but I’m not following all of those connections.

So normally, it’s better if all of your monitoring goes through the mixer because there will be latency (delay) through the computer. If you need to, you can use splitters to send the mixer’s output to the computer and also to monitors or a PA system, etc.

If you do want to monitor the computer, turn-on [u]Software Playthrough[/u].

The main out is connected to the mic in of computer

The mic input is “wrong” for your line-level connection. It’s too sensitive, the mic input is often mono, and usually the preamp is low quality. You can connect to line-in on a regular soundcard or if you have a laptop with no line-in, you can get a USB audio interface with line inputs. The Behringer UCA202 is popular and inexpensive. The downside to the UCA202 is that there is no recording-level control. Or, there are lots of higher-end audio interfaces with switchable mic/line inputs. (These better interfaces have XLR mic inputs for stage/studio mics. They don’t work with “computer mics”.)

Thank you DVDdoug for you input. So as per your recommendation I bought the UCA202, and thanks to Amazon, it came overnight.
But I am still where I started. I have attached a sketch of my arrangement.
The issue is, I can hear myself on headphone and can record, but I can not hear the background soundtrack through the mixer headphone. But that is the one giving me true voice feedback, if I use the headphone from UCA202 or monitor, it gives massive latency and also it is not giving me the true sound.
So bottom line is, how can I hear the background soundtrack through mixer headphone? I tried all speaker/mic setting in Audacity. None seems to be working!!

Thank you so much for your help!