Check cables and connections to see if:
1. Outputs are driving inputs and inputs are fed from outputs.
2. Signal from the source(s) is getting to the 460.
3. The signal chain after the 460 is functioning.
4. Check if the LCD display is illuminated.
5. If signal is present, and the downstream system is operative, check the level settings at inputs and outputs to ensure that they are not muted or attenuated sufficiently to make the 460 appear to not be functioning.