Thanks Ross, I've just seen your email.
Well you're right, those overload lights should flash if your signal is high enough and the trim setting is up full. The lights monitor the level directly after the pre-amp and trim control, so are unaffected by any assignments or track arming.
Before drawing conclusions though, I would check there is at least some signal coming in as it may be ok, but just not strong enough to reach the input overload threshold. Two ways to check:
1. Assign the input to a track and arm it.
You should see the track meter bar moving if there is a signal. The amount of movement will just depend on the trim control.
2. Assign the input to the stereo bus, confirm the Monitor Select option is set to Stereo, and raise the main stereo fader.
You should see the L/R meter bars moving. The amount of movement will depend on the trim control and main stereo fader (and also the input level control in the mixer screen, but if you've done a factory reset, that should already be set correctly).
If there is no or little movement, there's something wrong with the mics and/or cabling to them. Do the mics need phantom power? If so, that is only available on the XLR sockets, and it needs switching on for the corresponding bank of 4 (inputs 1-4 or 5-8).
Keep us posted.