Lead Developer
I would need some more information to help.
What steps did you take right before this happened?
Installed a caching plugin perhaps?
Restarting from scratch is never necessary with WordPress unless your database is deleted (not easy to do).
Documentation: http://docs.generatepress.com/
Adding CSS: http://docs.generatepress.com/article/adding-css/
Ongoing Development: https://generatepress.com/ongoing-development