Everything looks alive — waveforms moving, meters bouncing — and the room is silent. The signal is dying somewhere between the software and the speakers. Walk it out of the building in order.
Tinny sound from the laptop = your software is pointed at the wrong sound card. Audio settings → output device → pick the controller. This is the cause more than half the time.
The big RCA or jack sockets on the BACK labelled MASTER — not the headphone socket, not BOOTH (if your unit has one, it has its own volume that may be at zero). Check the cable's actually seated both ends.
MASTER volume knob up, the channel fader up, the crossfader on the correct side, and the channel's trim not at zero. Watch the master meter: if it lights, the controller is delivering — the problem is beyond it.
Active monitors have a gain knob round the back and a power switch. Volume up, right input selected (many have multiple inputs), and test with a phone into the same cable if still dead — that isolates speaker vs controller in ten seconds.
Different RCA cable, then a different output (headphone out to the speakers just to test), then a different speaker. Whatever component the silence follows is your fault line.
Sound only travels one road: software → sound card → master output → cable → speaker. There's no magic in it — silence means one gate on that road is shut, and testing in road order finds the gate without guessing.
Fixed it? The manual this came from covers the DJ controller the same way — every control, every failure mode, in plain English with diagrams. The Complete Rig — all four guides — £39, instant PDF.
Get the manual → £39 Or keep using the free stuff →