This is an issue I started to encounter some weeks ago, I think it is somehow related to the P.149 addon, do you own this? Specifically in this addon, com radios are default to off and turning them on and increasing the volume always works, but when doing the next flight with another plane, COM volume is always set to Zero and I cant hear anything.
Transient fix for me: I did bind the command “increase COM1 volume” to an unused key and keep hitting this key until I can hear ATC again. Not a nice workaround, but better than silent ATC 
For some planes, the knob works in the VC, as an example the FBW A320Neo, there I simply turn up the volume. In the TBM in contrast, the knob in the VC does nothing, there I use my assigned key.