I did reinstall UBUNTU 14.04 after having some issues with grub, the problem is that I can't access to my windows 7 anymore as the grub menu shows only Ubuntu partition. P.S/ during the reinstallation of ubuntu, I did choose 'erase and reinstall ubuntu .... ' instead of install 'ubuntu alongside ubuntu...' Windows was always in dual boot with Ubuntu but now I can't access to it. So please help me
Have you checked, if the Windows partitions are still available. For instance in you file-manager (nautilus) or a partition tool like "disks" (not sure about the name, as I run a German version) or gparted.
If the Windows-partition are gone - sorry, but you lost Win.
If the Windows-partition(s) is/are still on the disk, open a terminal and run
sudo update-grub. Copy the resulting output to an editor (gedit) and save it.
Then try a reboot and see if the grub-menu has changed. If not, paste the output from above here.