Can't view site or log in says password incorrect

I can’t view my site a message appears like this:

“Not Found

The requested URL /index.html was not found on this server.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.”

My domain name says it is still running. I tried clearing my history. I viewed the login trouble page but I am confused by certain instructions.

When I try to log on it says my password is incorrect. Have I been hacked?

I am trying to figure this out but I am new to wordpress so I am very confused!
Please help, thank you!!