Visit site and direct to 404 error

Hi everyone, I have just installed WP and this is my first time using WP. However, I am having trouble accessing the site.

I have created a folder ‘blog’ to store wp pages but after installing, when I type mydomain/blog, it points to a 404 page. I have rechecked everything I can: MySQL database, turning the file attributes to recourse, deleting the .htaccess file etc, but none of that work. I was able to access the login page by typing mydomain/blog/wp-login.php but then it points to 404 page again after logging in. Eventually, I was able to access the dashboard, by going direct to the url mydomain/blog/wp-admin/index.php. However, when I was at the dashboard, I tried to point to ‘Visit Site’ and it points to 404 error page again. I have no idea how I can fix this.

All the above happens before I customized my site, nor add any theme or plugins.

Can some one help? Thanks a lot.