When I try to install any recent version of Ubuntu, the screen shows some green and purple mess (like analog TVs when thers no signal). Then, a black screen. I guess it keeps booting in live/install mode. But I can't see it. I tried installing from CD and USB, I tryed changing some BIOS settings... I installed older versions, like 8.04, and it worked, but after updating the system, it crashes again. That's why I discovered that upgrading Nvidia drivers, made system show a black screen again. After that, I unplugged the Nvidia card and installed 12.04 with onboard card. It worked perfectly. Then, I plugged Nvidia again and system booted, but only showing that black screen again. I keep working with onboard card, so far... The nVidia is a GeForce 8500GT.
Try to boot a live CD or from an USB and press F6 on the first loading screen of the CD/USB. Choose 'nomodeset' with your arrow key and try to install the system again.
Otherwise hold the shift-key when booting the installed system and try to edit the Grub entry by selecting "Ubuntu" and pressing e.
If you don't know how to do this use the wiki or let me know.