Hi whoever will read this!

I've been using this pc daily for a while now; and this never occured
I came back home, tried to start my pc unplugged, but it didn't boot up. When I actually plugged it, the battery level showed "9%, plugged and not charging".
So I went online to check what I could do: I pressed the pin-button to reset the battery (since it's built-in), tried to update the BIOS (but couldn't, not enough battery when I had to be at least at 30%), then Power Reset by pressing the power button for 30 sec... Didn't work either.
Could you guys help me what happened and how to fix it, if I can?
THANK YOU