My computer doesnt start- stuck on boot

Hold power button until the system turns off. Wait 5 seconds then press the button to power on as normal

Thank you!
I did as you wrote, but it Is running [ok ] lines again... :(
Is there a way to attach here a photo of the screen? So you can see all the lines..

Have tried to restart it again as recommended and this is the last line I have recieved:
[ ok ] started GNOME- Displayed Manager.

Can you pls tell me what can I do?
Thank you.

Can it be that it cannot boot due to lack of space??
Is there someone who can help??

"Can it be that it cannot boot due to lack of space??"

Yes, in some cases a full hard disk can prevent correctly booting.

What you can try:

Press ctrl-alt-f2
This should open a virtual terminal with a login prompt.
Enter your username, press enter and when asked for the password, enter it and press enter again.

Now you have a terminal where you can issue cli commands.

What output do you receive for the command

df | grep "/$"

For closing down the computer from within a virtual terminal use the command

sudo poweroff

also run:

sudo apt clean

When you are able

It doesnt let me open the virtual terminal.. i enter the recovery mode and then root

/dev/sda1 479595176 457240116 0 100%

Sudo apt clean doesnt do anything

Execute the command

sudo du -schx /*

This will take a while for completion (maybe a minute) and will then show the directories with their space usage.
What is the directory with the highest number shown?

Home 413gb

But it seems to be stuck..
Has written also 4 lines like this one (with different file/directory name):
Du: cannot access '/proc/841/task/841/fd/4' : no such file or directory

Ok.. sorry- it has finished with 437 total

It seems that you have stored too much in your home directory.

If you already know a big file in your home directory that you will not miss (because it is stored also somewhere else), delete it.

If you need to identify the file name first, repeat with the commands

sudo du -schx /home/*

and

sudo du -schx /home/taloola/*
(or similar, depending on the output of the previous command)

Finally, if you have identified a bug file that you can delete, remove it with the command

sudo rm /home/username/directoryname/subdirectoryname/filename (insert the file name accordingly)

How much gb should i remove? (Minimum)
And how to do so? Like this:
Sudo apt-get remove /home/taloola/Torrentz
?
Or
Sudo rm /home/taloola/Torrentz

Is removing the Torrentz folder will be enough?

You should aim to remove at least 45 GB (that is around 10% of the disk size)

If you want to delete the whole Torrentz folder with all its contents, then the command is

sud rm -r /home/taloola/Torrentz

How can I see the list of flies the folder has?

And regarding the bug- how do I identify a bug?
Sorry for the ignorrance and thank you so much for your help!

Thank you so much, Andrew and Manfred!!!!

Now, one last question:
Is it recomended to format the computer and then install the latest lts version or upgrade, as it suggests me to do?

So, apperantley my computer did not start due to lack of space.

Thanks Manfred Hampl, that solved my question.

For the question about upgrading or a new install see also https://help.ubuntu.com/community/EOLUpgrades#Upgrade_or_fresh_install.3F