Loss of Radio Comms (VoIP)

I suspect this may be a curly one but I will be greatful for ANY clues. I have a 99% radio TX/RX comms failure. I can tune to and listen to ATIS reports, I can hear the tower and other flyers, I can sometimes (if Im lucky) talk to the tower, but when I commence taxi or on take off I loose the ability to talk to the towr or other flyers. Nav comms NDB/VOR/ILS all work so does data as I can see all other players. I have deleted or disabled virus programs (during various FSX installations) all to no avail.

Any help or clues appreciated.