Welcome to Roku Community.
To assist you further, may I ask if you have received an error message when entering your email address on the activation screen? Also, have you checked that your email address is spelled correctly and that you have a stable internet connection?
If you already have a Roku account, log in using the email address associated with your account. If you are creating a new Roku account, use a valid email address to associate with your Roku account in order to manage your account and receive important account notifications.
Please provide me with more information, so we can help you resolve this issue.