No HDMI audio when connected to screen

Audio over HDMI does not work if I keep the Laptop lid closed while starting Windows 10. The LG screen is not recognized as an audio device in Windows. But everything does work, if I keep the laptop lid open while starting Windows. It continues to work if I close the lid afterwards, unless I have to reboot again. I already installed newest drivers, newest BIOS and checked that there are no hidden devices in Windows' audio settings. Also I don't think it's a faulty HDMI cable. Does anyone else have that problem? Is there a fix?

Laptop: Inspiron 7706 2n1 Screen: LG 4K with speaker OS: Windows 10 64 Bit