title: WordPress redirects to not found page
body: <p>I have installed a WordPress on my hosting. Everything works fine, and then crashed! I go to</p>
  
  <p><code>mywebsite.com/wp-admin</code></p>
  
  <p>and WP redirects me to url (for login)</p>
  
  <p><code>mywebsite.com/wp-login.php?redirect_to=mywebsite.com2Fwp-admin%2F&amp;reauth=1</code></p>
  
  <p>The URL is ok, but the content is 404 error page!!!</p>
  
  <p>I didnt install any plugin or theme. There were not any changes in file system (new files o modified files).</p>
  
  <p>I tried removing .htaccess file, renaming plugins folder, theme folder, but it didnt works. The fields that contains web url in wp_options table are fine.</p>
  
  <p>The WordPress version was 3.9.2. I downloaded version 4.0, upload it via FTP, overwriting every file. I tried to log in, and WP wants to update DB, I did it, and then 404 error again...</p>