How to clear all processes/memory in linux?

Question

linux

I have 2 OS on my computer, Windows and Linux. While using Linux, the lights were turned off, 3-4 times, now, when I try to start from Linux, the Ubuntu icon loads for a couple of seconds, and then everything freezes.
I tried: 1) run ubuntu with the nomodeset key, to reinstall the drivers, for which I received "UEFI secure boot enable"
2) Many different long and short commands, to clear the cache / memory, stop / restart processes, for which there was a single error No space left on device.
3) I tried to find out which folders load the memory the most, through the command I sudo du -h -di /went to the "/" path, which eats the most memory and "inodes". The command sudo du -h / , however, leads me to the /dev/nvme0n1p6 folder, which also eats 125gb out of 125gb and avail - 0%.
I've been scratching my head over this all day and don't know what to do. On the one hand, there are quite valuable files, data, projects on Ubuntu, on the other hand, such a problem. If anyone has come across or knows how to solve it, please write as detailed as possible, I'm completely new to Linux, each action is given with great difficulty

Answer 1

Thanks to all! I did not understand the error, I had to reinstall Linux