[boot direct Windows]

If Windows is reinstalled, the boot choices are tossed out and Windows is the default. You probably have to reload Ubuntu on a second partition--after the reinstall of Windows. Make sure then that you save all the GRUB details in case a Windows update or service pack overwrites it. I think you'll then have to use an Ubuntu Live CD to replace the GRUB environment if this happens. Of course backup your personal data.

I'm still not clear about what is to be done.

Will I have to reinstall Ubuntu? Or is there something that I can do after booting via the Ubuntu Live CD to restore GRUB?

And how do I go about each of these?

Put in live CD.
use code:
sudo fdisk -l (small L)
Find Ubuntu sdax number (we will use sda5 for this post.)
Open disk utility and click on hard drive on left and the click on sda5 and
choose to edit Label if you do not have one. Make a label (lets say you choose to type in lucid for this post)

Open a terminal and code:
sudo mkdir /media/lucid
sudo mount /dev/sda5 /media/lucid
 sudo grub-install --recheck --root-directory=/media/lucid /dev/sda
sudo umount /media/lucid

Restart and choose Ubuntu when boots up code:
sudo update-grub

Thanks Richard Garvin, that solved my question.

Thanks a lot Gavin :-)

i have dell inspiron 15 laptop with windows 7 and then i install ubuntu 9.10 and now i get error:

Grub loading.
The symbol ' ' not found.
Aborted. Press any key...

i know this is the problem of grub loader and i tried the solution which u provide here but still i face same problem.

give me reply as soon as possible...

Ankit, here's a link to how to deal with GRUB issues:
http://ubuntuforums.org/showthread.php?t=1195275
Perhaps there's something there that can sort things out for you.