ubuntu 11.04 only boots into a grub prompt

Did you use Wubi or did you install from a booted liveCD and install to the system that way?

I booted up the computer using the live cd and installed from it.

At grub prompt, please let us know the results from these commands...
grub> ls
grub> search -f /boot/grub/grub.cfg
grub> search -f /vmlinuz
grub> search -f /initrd.img

You need to do it in the liveCD, not from the grub prompt

You can do this at the grub prompt,
This is to make sure Allan has installed properly, not into Wubi, and if
/boot is not on a separate partition, then the results will tell the
partition Ubuntu is (properly) installed to, then he can continue to
boot as follows....

grub> set root=(hd0,x)
grub> linux (hd0,x)/vmlinuz root=/dev/sdax ro
grub> initrd (hd0,x)/initrd.img
grub> boot

where (hd0,x) and sdax [x is a number] is partition Ubuntu's installed to.

Then after booting at terminal, he can...
sudo grub-install /dev/sda

Hope this helps.

Thanks guys. OK from the grub prompt this is what I get when I follow your grub commands.

grub> ls gives me:

         (memdisk) (hd0) (hd0,msdos1) (hd1) (hd1,msdos1) (hd2) (hd2, msdos5) (hd3) (hd3, msdos1) (fd0)

With reference to the three search commands I entered, they all came back with the same result: hd2, msdos5

I'm not going to try anything else until you guys come back to me with more specific results assuming the above is sufficient.

Allan, that's why I sent the first message first (not the second with it). You have another disk hd2 (which you did not say earlier) that has a linux OS on it rather than just on one disk. This makes a difference.

So to boot ubuntu, ensure all disks are connected, and type in

grub> set root=(hd2,5)
grub> linux (hd2,5)/vmlinuz root=/dev/sdc5 ro
grub> initrd (hd2,5)/initrd.img
grub> boot

If same error, change to
grub> set root=(hd3,5)
grub> linux (hd3,5)/vmlinuz root=/dev/sdd5 ro
grub> initrd (hd3,5)/initrd.img
grub> boot

or
grub> set root=(hd1,5)
grub> linux (hd1,5)/vmlinuz root=/dev/sdb5 ro
grub> initrd (hd1,5)/initrd.img
grub> boot

[reason: BIOS sometimes gives wrong 'x' in (hdx,5) sdx5 where x changes with multiple disks]

Then after booting at terminal.....
sudo grub-install /dev/sda

[be aware then that your disk that contain the ubuntu OS must always be plugged in ensure all OS (including windows) be able to boot]

Good luck.

Oh, after 'enter' at last command "boot", there may be a 30 to 45 secs delay before anything kicks it. So wait.

[reason: there is a 'rootdelay' (to ensure disks are detected) when booting to usb disk OS]

God I'm an idiot. I thought I had said that I had more than one disk. I have three. One is WinXP, One is a data disk, and one is Ubuntu. I also have an external. At any rate I'll give your instructions a go and let you know.
Thanks.

Hey Goh Lip. I'm writing this from Evolution Mail in Ubuntu. Your method worked like a charm. Thank you. You are a gentleman and a scholar. Probably good looking too. lol
Thanks again

I still have to reboot and check that it boots from the boot log, but I expect it will. If not I'll be back. Terminator reference there. lol

Good to hear, Allan.
All of us have been an idiot sometimes, hopefully, just not too many times. :)
Welcome and take care.