So, I'll explain the problem, but first I want to cry aloud PLEASE HELP!
I've used Ubuntu 12.04 for more than half an year and everything is set up just the way I want it. But I did a stupid mistake - I installed Proprietary ATI Driver fglrx.
Now the system boots normally, but after I choose to launch Ubuntu the screen goes black and my monitor doesn't receive any signals.
I tried some guides in recovery mode, but it's not working. Finally I started live cd and replaced files in /usr/share/X11/xorg.conf.d/ with original files. Still not working.
Please give me any ideas how to remove this killer!