Squawk Box cant work out whats wrong trouble

Hi guys, I have decided to give Vatsim a go via squawk box. I have downloaded and followed tutorials on install etc, and all seemed to install fine. When I start fsx I choose a gate and start SB.  Squawkbox says I have connected succesfully, It shows the atc channels on the right but I tune active tower channel and nothing happens. I do not hear anything at all from atc, the bottom right says text only and when I hit the PTT button it buzzes. I have calibrated my mic and it says works fine. Any help? I have uploaded plans also and scenery aircraft disappear but no change otherwise. Thanks in advance!