If you're logging into an account after 2 years or more, you will not be able to access the pound for 3 months. During this time, you will not be able to adopt, abandon or transfer any pets. This measure is in place to protect against the unauthorized access of accounts, ensuring that pets cannot be stolen or traded in the event an account is compromised.
You can still gain a new pet (given you have a pet slot) by creating a new pet, hatching a draik egg or transforming a krawk petpet in the Fungus Cave.