I would back up the hard drive image to a USB flash drive. However, given that you write that your hard drive has a problem, who knows how good that image will be. You should have made the backup when you first received the laptop.
Hi, I just bought a Vostro 4580 with Ubuntu 14.04. It has a HDD problem, and Dell is about to send a new HDD, but empty, no OS installed.  Is the Ubuntu for Dell a specialized version, or is it the same with the one in Ubuntu website?  I remembered in the first boot, I was asked if I wanted to make a backup image to a flashdisk. Can I use that to install Ubuntu? Or I should just download from the Ubuntu website?  Thanks,
Ubuntu 14.04 image for Dell Vostro 4580