Hi Timo,

There can be multiple reasons or it. I would suggest you to follow the below steps to solve this problem:

1. Check your Driver
Normally you would open Control Panel > Sound > Under Playback and Recording tabs, Select and Set Defaults. Additionally or alternatively, you may also have to try this: Click Start > Type Device Manager in Start Menu Search Bar > Hit Enter.
The Device Manager will open. Expand Sound, Video and Game Controllers. Locate your audio device. Double click on it to open its Properties box. See whether the driver is installed and the device working properly.
In the Driver tab, click on Update Driver. Click OK. Else you may have to uninstall the Driver (but DONT delete it) and then in the Device Manager > Action > Scan for hardware changes. This will reinstall the driver.

2.Check your sound card
Ensure that your Windows PC has a sound card, or sound processor, and it’s working properly.

To check this, select the ‘Search’ option from the charms-bar, type – Device Manager’ and click ‘Settings’. Open Device Manager, double-click Sound, video and game controllers to expand that category. If a sound card is listed, you have one installed. Laptops and tablets do not usually have sound cards. Instead, they have integrated sound processors, which appear in the same category in Device Manager.
See if it is working properly. If Device Status shows that the device is working correctly, the problem showing up is due to sound settings, the speakers, or the cables.

3. Setting correct audio device as default
Type ‘Sound’ in search and select ‘Settings’. Choose ‘Sound’. Under the Playback tab section you will find multiple audio devices; appearing as speaker, followed by the name of the device. You will also observe that the default device shows a green a check beside it, labeled as Default, if you have multiple devices.

If the wrong audio device is listed as the default audio device, simply choose the correct device and click ‘Set Default’ button. Restart your PC!

4. Check if the Speakers and headphones cables are connected properly
New PCs these days are equipped with 3 or more jacks including,

1. a microphone jack
2. line-in jack
3. line-out jack.

These jacks connect to a sound processor. So make sure your speakers are plugged in to the line-out jack. If unsure which is the right jack, try plugging speakers in to each of the jacks and see it produces any sound.

If you’re using headphones, make sure speakers aren’t plugged into the line out (headphone) jack of your sound card or PC.

5.Sound and Audio Troubleshooter
If all fails, you may bring in and use the built-in Troubleshooting tool in Windows 10 / 8. The tool may automatically fix audio recording problem.
To open the Sound and Audio Troubleshooter, bring up the Control Panel by pressing Win+X in combination and selecting Control Panel. Then, under System and Security click Find and fix problems. Or else, simply right-click on the Speaker icon in the Taskbar notification area and select Troubleshoot sound problems to open the Sound and Audio Troubleshooter.

When done, choose ‘Hardware and Sound’ and click on ‘Troubleshoot audio recording‘ link.

I hope this helps.

Regards,
Lokesh