The internal microphone doesn't work on my Dell Inspiron 14 7440 running ubuntu, though it is recognized on windows and I remember it working before I reinstalled the ubuntu system. When I open sound settings, the app doesn't recognize the internal microphone:

I ran alsamixer (newest version) in the terminal and didn't see the internal microphone, this is what it looked like (this screenshot shows all devices listed in alsamixer):

I also looked at pavucontrol and the app shows the internal microphone as "unplugged":

How can I get the microphone working?

Update: I tried plugging in a headset and plugging it out. When I plugged it in 2 microphones showed up, one called "headset microphone" and the other just called "microphone", screenshot:

But when I unplugged the headset both microphones are gone, does it mean that my laptop recognizes its internal microphone when a headset is plugged in? Also when I switch to the one just called "microphone", speaking to the headset microphone doesn't make the bar move as much as patting the laptop, so the "microphone" should be the internal microphone.