Apex legends wont launch?

In addition to the troubleshooting steps posted on this thread (thanks everyone), you should first check your machine meets the Minimum System Requirements

If you are sure your machine does meet the minspec, you should take a look at the following link as there are a lot of collected steps there that have been reported as helping prevent crashes: 

Community Crashing Troubleshooting Guide

Thanks again to all who have posted steps that have helped.