Ubuntu 20.04 doesn't boot up - num lock blinking

I'm dual booting Windows 10 and Ubuntu 20.04. But today, when I turned on my laptop, I saw the plymouth boot screen and then the screen was blank, with a small "line" at the upper left edge of the screen. One thing I noticed was blinking num lock key.

After about 10 minutes, the num lock key stopped blinking and the "line" or cursor too. It stuck for about 30 minutes now.

What I've tried:

• Reboot

• Use older kernel

EDIT

When I press the power button, Ubuntu will shut down.

Solution 1:

Yeah, it was because of full disk usage. If you have these issues too, here's how to fix it:

1. Boot into recovery mode.
2. Choose root console.
3. Use the command line to find and delete large files you don't need.
4. Reboot and check if it helped.