Cobra PR4100-2WXVP 2-Way Radio "mute incoming" Questions

...incoming signal. However the squelch feature can also cause weak signals to cut out and not be understood, so the Monitor function provides a way to disable the squelch in those circumstances. It ...

What makes it suddenly go deaf and mute? I used this rig for many months at approx 30 watts into a less than 2:1 matched caged dipole with no problems on PSK mode. I turned it on one day, and couldn't