The free version or the trial version? The trial version DOES require a key, a trial key. When you downloaded the software, you will have entered your email address to create a temporary quest account. As part of the download, you are then emailed a trial key that expires on. I downloaded this myself a few weeks ago, i received a trial key in the e-post, you cannot install it without one. You need to find that email.
Be warned tho' the date on the key is hard coded, of you install it on a fresh machine after this date, the key will still be expired.