Admin password not working

This is driving me crazy today I need help!

Suddenly my password is not being accepted to log in to the dashboard. I have tried resetting the password, I go through the process, and login. But when I log out and try to log back in it tells me the new password is invalid. I have tried resetting the password three times now and it still has the same problem.
Also if I try to live preview a theme instead of the site preview I see the login screen saying the session has expired, asking me to login again, but the password is no longer valid.
I have tried clearing cookies and browser cache but nothing changes.
Any help would be greatly received before I go insane!

Thanks