404 Error Page When Trying to Load Main Page?

I just uploaded a custom theme to my client’s WordPress install, and most of it works beautifully–except for the fact that when I try to go to the main page, it throws up my 404 error page instead.

The layout loads fine, but it won’t load any posts on the main page. When you go into the different categories, however, it works fine and it finds the posts, so I know the posts aren’t gone.

The last webmaster had a static WordPress Page configured as the landing page (I have no idea how he did that), so I’m wondering if there’s a setting somewhere in the Dashboard that I missed. But I have no such Page configured and no such Page called for in my custom theme. For some reason, it kept loading the static Page on my theme, and when I deleted the Page, it started throwing up the 404 error message.

I have deactivated my theme for now, until I find out what the technical bug is. Any help would be greatly appreciated!