We'd like to know more. What happens when you try accessing the Video Manager? Is there an error? Also, let us know if you're using YouTube Studio or Classic. Keep us posted.
Thanks for the info. Have you tried clearing the browser's cache & cookies to see if that fixes the issue? Here's how: https://goo.gl/e2dYZt . Also, try using a different browser or Incognito mode to check if that makes any difference. Keep us posted.