What does "image backup" mean. If it is truely an image, it is probably not in a format to boot from. That is not the same as a mirrored copy. An image is usually a single (or multuple spans) file which contains a compressed "image" of a logical drive. An image is used to restore (or rewrite) a computer from the image taken at a specific time. Dell places a restore file in a second (partition) logical drive, to restore the base operating system. If this is the type of image, none of your data or self installed software will be in that file, unless you have created a new "image" since you have owned the computer. What software is being used to create the image.
If it is a bootable (2nd) drive, are all of your files on it? If it is a mirror of the 1st boot drive, when was the mirror created? Is it a raid?
Sorry to ask a bunch of dumb questions but just getting a new HD is rarely as easy as it seems.