Dell Latitude C840 - Manual (Page 107)

3. Click the Properties (wrench) icon.
4. Click the Audio tab.
5. Click Enable S/PDIF output.
6. Click Apply.
7. Click OK.
Enabling S/PDIF in the Windows Audio Driver
1. Double-click the speaker icon in the Windows notification area.
2. Click the Options menu and then click Advanced Controls.
3. Click Advanced.
4. Click Enable S/PDIF.
5. Click Close.
6. Click OK.
NOTE: Enabling S/PDIF in Windows disables the sound from the headphone connector.