Recording Line In, waveform visible, no playback


I am quite familiar with audacity and its capabilities, but I am having trouble playing back recorded signal from line in.
Audacity version 2.0.3
Intel motherboard (line out, line in, microphone) with old Pentium 4 1,7 GHz processor
Signal from a guitar combo with a line out output
Sound driver directly from Intel.

The problem is: when I record from a microphone input with a microphone, everything records ok and plays back.
When I use the line out from the guitar combo everything records ok, waveform is visible - matches the guitar playing.
But I can´t get it to play back. I press play and only a slightly audiable sound comes through the speakers.
When I record one track with microphone and one with line in, alongside (multi-track) only the signal from microphone can be properly heard.

I have not tried to connect the line out to microphone in. That did not cross my mind, in next step I will try that.
Raising volume on the Line in track only overdrives the signal.

Any thoughts?

Thank you

Did you bump the volume control to the left of the blue waves by accident?

The microphone signal is probably one single mono track, but the guitar is probably two tracks, right? Two blue waves?
Drag-Select a small portion of the guitar signal and Magnify Selected (Control-E). Do that a number of times so you can see the individual ups and downs of the blue waves. Are they mostly going the same direction or opposite? Koz
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