I installed Ubuntu 11.10 on my laptop alongside Windows 7, and the GRUB screen was purple. After that, I installed Ubuntu 10.10 and the GRUB screen was black. When I decided to uninstall Ubuntu 10.10, the bootloader didn't change and I was greeted by a black Terminal screen. How do I remove the Ubuntu 10.10 GRUB bootloader and use the Ubuntu 11.10 one?
This is what I think has happened. It will help you to learn from the experience as we all learn one way or another.
When you installed 11.10 it put its Grub into the MBR (Master Boot Record) of the hard disk and looked for its configuration files in the 11.10 file system. And so you get a purple background to the Grub Menu.
Then you installed 10.10 and it put its Grub into the MBR and so you got a black background to the Grub menu.
Now that you have uninstalled 10.10 you get a Grub prompt because the 10.10 Grub is the controlling Grub and it cannot find its configuration files in the 10.10 file system.
If you had run sudo update-grub from 11.10 you would not now have this problem for that command would have made the 11.10 Grub as the controlling Grub. This link will help you fix it.
Note point 13, Reinstalling Grub 2 from a LiveCD. Follow those instructions and you will fix your problem. To make it easy to avoid this issue in the future I have included this link:
I have found Grub customizer most useful for avoiding this problem and for configuring the Grub menu. I recommend it.
With thanks to Daniel Richter a Ubuntu Forum staff member.