So I managed to get GUI back without any command line typing. I did nothing, just hit
Ubuntu option the next boot attempt. Just didn't let GRUB stopwatch to reach 0 and didn't use arrows in GRUB menu, just hit
Enter. Very strange.
First of all, I remember when it happened. I turned on the computer and left my room to do other things. Before it I always manually selected in GRUB menu what system to load, either Xubuntu or Windows. I never let GRUB stopwatch to reach 0 and boot itself, I always hit
Enter earlier. So when I came back to computer I saw the command line prompt instead of GUI.
I didn't know how to restart Xubuntu safely from the command line, so in this situation I just hit the restart button. The following boot I immediate used arrows in GRUB to go down the menu (up to Windows XP option) and then go up to select Ubuntu again. Just to stop GRUB stopwatch. Then hit Enter. But got command line again. I again reset the computer with the reset button.
This time I switched to Windows, surfed the Internet for answers, wrote this question. Found this 7 pages thread http://ubuntuforums.org/showthread.php?t=1570540. A user experienced the same problem in 2010. The main solution is on page six http://ubuntuforums.org/showthread.php?t=1570540&page=6&p=9935242#post9935242. So I did the same.
I tried to boot again but this time I didn't use arrows. I just immediately hit
Ubuntu option in GRUB. And I got GUI. Xubuntu is installed but GRUB's option is
Xubuntu also fixed some crash when I entered GUI:
xserver-xorg-core 2:1, 13,3 - Oubuntu6
Xorg crashed with SIGABRT in raise()
So my conclusion is: if you want Xubuntu, immediately hit
Enter in GRUB menu. Don't let stopwatch to get 0 and don't use arrows. I you want Windows, choose a Windows option using arrows and hit
Enter. Isn't it ridiculous?