Ununtu doesn't want to log in. It throws some error and goes back to the log in screen. It's same with the KDE.

Thank you for taking the time to report this issue and helping to make Ubuntu better. Examining the information you have given us, this does not appear to be a bug report so we are closing it and converting it to a question in the support tracker. We appreciate the difficulties you are facing, but it would make more sense to raise problems you are having in the support tracker at https://answers.launchpad.net/ubuntu if you are uncertain if they are bugs. For help on reporting bugs, see https://help.ubuntu.com/community/ReportingBugs.

I don't remember user and password what i can do

You can do this: http://www.psychocats.net/ubuntu/resetpassword

or

To discover your user and restore (change) the password you can:

Start the pc the when you see the GRUB row...

Press ESC and choose the recovery mode

You will get to a prompt. You are root the superuser and can do anything you want
So enter the following command:
Your system will boot up to a passwordless root shell.

Type in grep -i 1000 /etc/passwd

The system must show a row with your user name at the start of the row
for example:
danilo:x:1000:1000:ubuntu,,,:/home/danilo:/bin/bash

Here my user is danilo

Then to change your user password type in:

passwd username

or

passwd -d username

change username with your real user

Set your password.

Type in:

reboot

or

reboot -f

Hope this helps