I am now unable to open Lightroom 5.7 - when I try to open the program I get a message that the "Lightroom 5 Catalog" has already been opened by another program. All previous versions of Lightroom were previously deleted from my WIN 8.1 PC.
With Lr closed go to the location where your catalog resides(By default it is Pictures/Lightroom)
Delete the .Lock file with the same name as your catalog.For instance in the Picture below it is Lightroom4 catalog.lrat.lock
In your case it will be Lightroom5catalog.lrcat.lock
Let us know if that helps