The solution to the problem is in two stages (from my experience, as it
always happens to me when installing ubuntu).

1. When booting the computer and the grub menu comes up press the letter
"e" (without quotes). That (as is written under the menu) will enable
you to edit the partition place your Ubuntu is installed.

2. The line to be edited is the first one with the (hd 1,4).

3. The numbers must be changed to be the correct ones where your Ubuntu
is installed.

4. The numbers mean which disk Ubuntu is installed - the first (or
primary) disk is always "0".

5. The second number refers to the partition on that disk where Ubuntu
is installed.

6. In all cases the first partition of a disk is "0".

7. So if you have one disk the number will be (hd 0,something) depending
on the partition.

8. If you have windows as a dual boot the Windows partition is usually
(but not always) (hd 0,0)

9. That's how mine is so the Ubuntu partition on mine is (hd 0,1)

10. You can play around with this ad infinitum, trying out different
combinations. When you get the correct combination your Ubuntu will boot.

11. If I remember correctly you change the combination each time by
pressing "e" to edit and after changing the combination press "b" for
boot to try it out.

12. When you are finally booted you have to permanently edit the grub
menu to remain with the correct combination for future booting.

13. That is done through the terminal and a text editor (with sudo) of
the /boot/grub/menu.lst file.

14. One last comment - you may also have to correct the combination of
the Windows HD reference in the "menu.lst

There may be a more "scientific" (correct) way of doing this but this is
how I've done it many times.