Post Receiving "PAGE 404" Error

Whenever I attempt to view a new post or even existing post I’m receiving a “Page 404” error or it says “OOPS! THAT PAGE CAN’T BE FOUND.
It looks like nothing was found at this location. Maybe try one of the links below or a search”

Can anyone help me? I even attempted adding a new theme & deleting the old one but it still says the same thing