During Ubuntu install, did you choose to have Ubuntu co-exist with other OS? Like Windows? If you can now boot into Windows and as I understand you can, try installing Ubuntu again but carefully select the right option, that is to have Ubuntu co-exist with Windows.
You might already have Linux partitions, since you had Ubuntu at one point in time, so you might want to delete those partitions if no data is there to keep, via the install Wizard, that takes care of the Ubuntu install. This will result in a clean install, for you.
EDIT: Ubuntu by default, I think opts for multi-boot setup. But to restore and not install again, you could try this link: Grub restore
Worked for me a few times when Windows 7 re-install changed the bootloader to it's own version.