not accepting login

i had been using wordpress successfully until this weekend, when suddenly after publishing a sales page when I went back in to edit the system indicated my user name and password were incorrect, however my admin information on GoDaddy verified that I was using the correct login. I am essentially locked out of my account and cannot get to the dashboard etc to fix my work. the URL that houses the sales page is coming up incomplete, missing both text and the “buy now’ button for customers.
How can I once again gain access to my account and work? thank you
(I upgraded to 3.12 this weekend if that is relevant)
Lucy