Logging in from my website

I just tried to login to edit my website and am getting an error message “invalid user name” “Lost your password”
The reason for wanting to edit the page was that I had the following message on my home page.

404! Danger, Will Robinson!
Somehow, you ended up in the wrong place, but don’t worry! Instead, try one of the following:

Hit the “back” button on your browser.
Head on over to the home page.
Use the navigation menu at left.
Click on a link in either sidebar.
Try searching using the form in the sidebar.
Punt.

Any help appreciated.
I am not sure I have the right version of WordPress selected above. I did upgrade last year.
thanks
Keith