Dell Latitude E6400 - no sound

Hello,

I have a Dell Latitude E6400 (Win 10 Pro, 64bit, Nvidia Quadro NVS 160M, IDT High Def Audio) and until now I did not recognize any problem with audio or else, but today as I wanted to start a call in skype, it was not anymore possible because of an audio device problem (I am not sure, but I think the audio has worked until I did not accept the call). After that I've made a restart, I've checked all drivers (which are up-to-date), downloads etc., I also re-installed the device, run the dell diagnostics, read related articles in Google about that, but I could not resolve the problem. In Device Manager, it says the device is OK, there is no problem with it. I see under Audio, Video and Gamecontrollers: IDT High Def. Audio CODEC and NVIDIA Virtual Audio Device (I tried to disable NVIDIA Device, but it has not helped me). So, I do not really know what I shall do...and I am not sure whether it is a software- or hardware-related issue. I really appreciate any help from you!

Thank you very much!