Ubuntu does not load

- open a terminal from applications > accessories > terminal
- first make a copy (on your desktop) of your menu.lst file typing exactly this: sudo cp /boot/grub/menu.lst ~/Desktop
(if your desktop has another name than 'Desktop', enter that name instead - you can copy and paste from here, anyway '~' is made by AltGraf+ì) (be aware that the terminal is case sensitive so 'desktop' is not the same as 'Desktop', and that when you type your password you don't see anything)
- type exactly this: sudo gedit /boot/grub/menu.lst
-type your password
-the file should open, go to the bottom, until you see the list of your kernels and search the one that says (for hardy):

title Ubuntu 8.04.1, kernel 2.6.24-19-generic
root (hd0,4)
kernel /boot/vmlinuz-2.6.24-19-generic root=UUID=ea1966d0-19be-4ed0-b62c-6d9aa5dd8edb ro quiet splash
initrd /boot/initrd.img-2.6.24-19-generic

anyway you have to search for ubuntu, not recovery mode and not memtest

- edit the line removing quiet splash so it'll be

title Ubuntu 8.04.1, kernel 2.6.24-19-generic
root (hd0,4)
kernel /boot/vmlinuz-2.6.24-19-generic root=UUID=ea1966d0-19be-4ed0-b62c-6d9aa5dd8edb ro
initrd /boot/initrd.img-2.6.24-19-generic

-save the file and close, now when you boot you should see the booting process.

-if you want to restore the original file just reopen it and add quiet splash again, or replace it with the file you saved before by: sudo mv ~/Desktop/menu.lst /boot/grub

hope it helps. cheers