This depends on when you deactivated it. 

Accounts can only be reactivated within 40 days after deactivation. After this period of time, the personal data of the profile are anonymized and not restorable. 

If you want to work as a Clickworker again, you will have to register again, but you can use your former data, including your user name, if it hasn't been taken by another user in the meantime. 

Click here if you forgot how to register.