Powers on as normal but with no sound.

First, check for simple issues such as mute accidentally turned on. Some Kenwood models have a preamp-only mode that turns off the internal amplifiers. It's buried deep in the menu options. Check for that and disable if necessary. Also disable any demo (demonstration) mode in the menu since that can also affect the amp's output. It's possible the head unit's amp is bad, but that's unlikely and especially unlikely to affect all channels at once. It's more likely a menu setting or a wiring/connection problem.

Following.. Mine was working just fine for a couple of years with no issues and suddenly happened the same, everything works just fine except there is no sound and no beeps either. I have no external amp. I use the head unit for the 4 speakers and the subwoofer output for a 12" Amplified Subwoofer, which didn't sound either except the "buzz" sound when I plug or unplug the subwoofer.