Can someone help me to fix my laptop's audio?

I don’t know what’s wrong with my laptop’s sound system since it’s not in mute state but it won’t produce any sound no matter how high the volume I set. It appears that some of my friends have used it and probably caused something in it but for some reason I can’t contact them in a moment. I’ve checked the ‘sound and audio devices icon’ from control panel and it seems normal as usual without any mute checks.

I’ve no idea what should I do next since I can still hear a sound from it yesterday so I think it’s not like my laptop’s sound system is being damaged or else.

I really hope someone can tell me how to fix this situation.