Hey Tilo,
1. Run Audio Troubleshooter for sound issues.
Refer:
Open the Playing Audio troubleshooter
http://windows.microsoft.com/en-us/windows7/Open-the-Playing-Audio-troubleshooter
2. Check and ensure that the speaker is plugged in tightly.
3. Unplug the device from the USB port and connect it to a different USB port.
4. Test your speaker configuration. Ensure that you have the best configuration set for your speaker.
Refer the steps from How do I test my speaker configuration? from the link below.
Sound cards: frequently asked questions
http://windows.microsoft.com/en-US/windows7/Sound-cards-frequently-asked-questions
5. Check the drivers. Ensure that you have the correct one installed for your sound card.
Select one of the options from the link below to identify the product.
http://support.dell.com/support/downloads/index.aspx?c=us&cs=19&l=en&s=dhs
Refer:
Update drivers: recommended links
http://windows.microsoft.com/en-US/windows7/Update-drivers-recommended-links
Regards,
Shinmila H - Microsoft Support
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