Try refreshing your browser, or logging in using incognito mode on your browser. If you still cannot log in you may need to reset your password.
On the Log In page, enter your email address and a Password box appears. Underneath the Password box, a 'Forgot Password?' button will appear.
Click this button and a temporary password will be sent to the email address you provided, which will allow you to complete your log in. You'll then be asked to change your password to one of your own choosing.