Press the PHONES SOURCE button on the Aurora(n). From here, you can choose any stereo source from: Analog Inputs, LSLOT (Computer Connection Method) or SD Card Play. Make sure that the appropriate source is selected here.
Still nothing? Go to the METERS page and choose the ALL I/O Meters. You can toggle between Analog Inputs and LSLOT Inputs by pressing the "Select" button. Are you getting meter activity for the input that you are attempting to monitor through the Phones? If not, try troubleshooting the problem with the signal source.
Still nothing? Power Cycle the Aurora and try again.