Hello Karen,
On the Adobe Media Optimizer login page, there is a "Forgot Password" link next to the Sign In button.
If that does not work for you, then the account may have been locked for some reason. You can ask your account manager to assisst, or contact technical support by sending email to <Media Optimizer user account>@support.efrontier.com (e.g. karens_username@support.efrontier.com) to get it reset.
Kind regards,
- Carey