LinuxQuestions.org - Out of frequency during boot and on consoles

On the weekend I installed and played Crayon Physics Deluxe, and when I closed it it caused some graphics problems. I thought nothing of it and shut down the system. When I next booted the computer it gave a warning about hard disk erros at first, then rebooted, and then just gave me an out of frequency error right after the BIOS splash screen.

As I did not know what to do and where to look for the root of the problem I eventually set up the system (Ubuntu 11.04) anew, and even completely formatted the partitions for / and /home, so that absolutely everything should have been as it was on day one. But since then, even though the partition for / had actually been deleted and then created anew, instead of the Ubuntu splash screen I continue to get this out of frequency error until the login manager appears. And what's much worse, I get it immediately as soon as I switch to any console with Ctrl + Alt + F2 or any other, so I cannot use any console.

Then yesterday Skype had a crash, and again the whole thing started, after rebooting I only got the out of frequency error, nothing else. So I set the system up again, but the situation is still the same, the out of frequency error up to the login screen remains, and it also remains on the consoles.

There is no problem whatsoever with any system booted from CD. As all actual data had been wiped during the reinstall, I suppose that the problem must be connected with grub 2, some misconfiguration in the boot loader - but I have no idea how to check or change what's there.

The graphics adapter is a GeForce 7025 with nvidia driver 270.41.06. The Ubuntu setup offers two drivers, this is the older one apparently, but it's the same thing with the newer one. The monitor is a PKB Viseo 230Ws at 1920x1080 pixels, H 67 kHz and V 60 Hz.