Really, there are things unexplainable.
Checked everything once again from the beginning, took the cover out, used the blower of my camera to be sure I was following all your advices ( I don't have the can), checked sound volume once again with and without earphones testing with my own recordings and also YT, where I was when sound was gone; saying this I mean that I tried different sound sources one by one, et voilá! Sound volume had gone back to the lowest level with the earphones. It's working fine now! Maybe some little dust which I could not see, maybe some "whatever-I-don't-know". Anyway I want to thank you all for your help. I hope this will be useful for somebody who comes after me.
Maga