Optiplex 7440 Line in - no audio / very very low issue

I've been playing audio from my phone through my Optiplex AIO 7440 PC for few weeks now via 3.5mm headphone jack to 3.5mm headphone jack without any issues.
Have to put the volume on phone to about 80% and audio on PC about 80% to be able to hear it and of course, having "listen to the device" being checked.

Last week, when plugging in the audio cable, the auto detect input pop-up didn't pop-up and "line-in" wasn't showing up in the Sound settings.
I had rebooted my pc and it came back but when try playing audio, nothing was coming through, even when putting all to 100%.
I checked all settings, all volume, changing between Mic IN and LINE IN via Jack info.
When I tried from my MP3 player, it didn't work BUT, when I put the volume low to about 10% then unplugged and plugged back in, audio started coming through then when put the volume up high, it worked. But tried the same from phone, barely works. When all at 100%, you can hear but just barely. Brand new cable as well.

Before I try to uninstall the drivers and reinstall, any advise anyone can give. 

Cheers

Brian