To reinstall Grub, you could follow these directions:
If you need help adding Windows 7 to your Grub menu, then how about downloading the Boot Info Script to your Ubuntu desktop:
Then open a terminal (Applications > Accessories > Terminal) and do:
That will create a "RESULTS.txt" file in the same directory from where the script is run, namely your desktop; please copy/paste the contents of the RESULTS.txt file to your next post, highlight the copied text, and click the pound/hash sign "#" graphic button in the Ubuntu forum message box so that the text will get "code" tags put around it. The results of that script will help clarify your setup.
sudo bash ~/Desktop/boot_info_script*.sh