Settings are contained in the LR catalog so most of what you want can be done by merely creating a new catalog and reimporting everything and never opening the old one, again.
As far as reinstalling LR, download and install the latest update for whatever LR series you currently have a license for. In other words, if you have LR 5, then download and install LR 5.7.1. Various updates to LR can be found at a link on the Adobe updates page:
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Creating a new catalog and reimporting to it is the easiest way to start over. However, you should be aware that by doing so you will lose any editing and organizing that you have done because unless you have exported edited versions the edits are no more than entries in the old catalog - the photos are unchanged. If you do want to retain your work, a better route would be to revise the old catalog and bring it up to date with the new folder and photo locations, as explained here: Can I simply move my main pictures folder to External Hard Drive?
i had photos all over the place including in Lightroom I moved them all to an external hard drive now I want to reinstall Lightroom but can't find the disc. How to wipe everything and just restart.
New catalog and reinstalling is not necessary if you have moved photos to an external disk and Lightroom can't find the photos. The instructions to tell Lightroom to find the photos on the new external disk are: Adobe Lightroom - Find moved or missing files and folders