How to format hard disk in Ubuntu 14.04?

Try to make a bootable CD or pendrive of Ubuntu and then choose Try Ubuntu option. That is try to run live ubuntu and then using GParted (Which is in-built) try to format the partition in which your other OS is.

To format your drive you want to boot up yur system using either a Ubuntu live cd/pendrive or a Gparted live cd/pendrive

You can get the Gparted iso file from here: http://gparted.org/liveusb.php#linux-method-c

Use Unetbootin to create a pendrive to boot up from. You can install Unetbootin with the following command:

sudo apt-get install unetbootin

You can also use the Ubuntu's Startup disk creator, but I have found Unetbootin to be more reliable for me.

When you have created your pendrive, reboot your computer. Remember to change the boot priority under the BIOS settings so that the usb is booted first.

If you chose Ubuntu as your OS to boot up from, select try Ubuntu and then under the search bar look for Gparted and run it. It will show all your installed drives. From there you can just right click and select format. Execute the operation and Gparted will format the drive. For Windows the new partition format should be NFTS.

If you used the Gparted iso to boot from, the process is basically the same.