I can't open Lightroom 5.5 after downloading it on my Mac.

I have a new Macbook air.
I downloaded a trial version of Lightroom 5.5 and now I can't open it. It just guides me through the "Install Adobe Photoshop Lightroom" every time.
Please help.
It does say something like "click this box" and then "you already have mplayerx installed", is it trying to open it through that or what the what?