Hi Wendy,
Here are some troubleshooting steps I'd like you to try on your Mac; please provide me with the results for each...
1. Check that the computer recognizes it as a USB device
- With the unit powered-on and connected via USB, open the System Report by click the Apple icon > About this Mac > System Report.
- In the left pane, click Hardware (if not already open) > USB.
- On the right, look for the DDJ-S1 and click it to see if the details are provided.
2. See if the OS recognizes it as a MIDI Device
- Open the Audio MIDI Setup app.
- Open the MIDI Studio window if it's not open; Window > Show MIDI Studio.
- See if the DDJ-S1 appears in the window with a solid color.
- If it does not appear or you feel this may be part of the problem, you can try creating a new MIDI Configuration.
- Click the drop-down (currently showing Default in the image above) and select New Configuration...
- Give the new configuration a name and click OK.
- The connected devices will be scanned and your DDJ-S1 should appear.
3. Check the audio device
- Open the Audio MIDI Studio app.
- Open the Audio Devices window if it's not open; Window > Show Audio Devices.
- Verify that the DDJ-S1 appears as an audio device on the left.
Please let me know the results for each section.