I'm really new to Ubuntu so although I've read the replies to previous similar questions, I can't understand what I need to do.
I installed Ubuntu 12.04 on my Mac with OS X 10.6.8 two days ago. Everything seemed to work fine except I'd get the black/purple screen mentioned here (My computer boots to a black screen, what options do I have to fix it?) every time I boot Ubuntu. Therefore as suggested, I downloaded propritary drivers for nvidia (there were quite a few listed). After rebooting the second nvidia driver update, my laptop refuses to boot beyond the grub screen and freezes with a black screen with blinking cursor. It doesn't respond to Ctrl+Alt+F1 so I can't bring up terminal to type in the sudo commands mentioned in other answers. I have also tried nomodeset to no avail. The same thing occurs if I try to reboot from USB.
If it helps, here are the specs for my setup: Graphics: NVIDIA GeForce 9400M Model: MacBookPro5,5
Any help would be greatly appreciated.