Installation has failed at some point. Then you tried installing and now it is failing earlier because your database is in an inconsistent state. Knowing the original error would be useful to see in which step the original installation failed. As you don't remember that for sure, you'll have to go step by step.
1. Locate this line and comment it adding two slashes ( // ) at the beginning of the line
Retry the installation and report back (copy/paste the red text as a comment) here.