If you are receiving this error below "404 - File or directory not found" it is basically a permalink error. Follow the step by step below:
1. Log in to admin page www.domainname.com/wp-admin
2. Click on Settings on the left hand side
3. Click on Permalinks
4. Simply click on save at the bottom to confirm the choice. Open a new tab and test your website pages. They should be able to open without issues. Please submit your question if further issues persist.