inputs dont seem to work on Virus TI

[Vorax]

• • I’m inputting a line level signal from the mixer carrying a vocal (I’ve tested this into an outboard fx unit, and a signal is definitely coming out of the mixer)
  • I have checked the virus is working by playing a preset patch (RAM-A 125>>INPUT<<) . I then go into the EDIT SINGLE ‘inputs’ menu and set the mode to ‘static’ and the input select to ‘L’ (I have carefully plugged the line level lead into the L input on the virus) – no sound comes out from the virus, even when I can see that the source sound is activating the mixers meters.
  • I can’t get any output, either thru the filters or vocoder, or no matter what I twiddle with!

Is it obvious to anyone what I'm doing wrong?