I installed Ubuntu 12.04.4 into my desktop PC (ATI Radeon HD 5570 Graphics Card, Monitor full HD LG W2240).
I tried to install ATI catalyst driver suggested by Ubuntu system itself. When I tried to reboot, it keeps on giving me on a black screen the message signal out of limits 74.9 Khz / 60 Hz. The same message is given when I try to boot from the safe mode. I tried to use the instructions suggested by this page but I couldn't achieve anything since it keeps on offering a login prompt where nothing is actually accepted.