Set up your cable box. Before you call your cable company, you should ensure the box is connected properly to the outside cable lines as well as your TV. This will speed up reactivation confirmation on your end.
Call your cable company. If you don't know the company's phone number, you can find the number on your most recent bill under "Customer Support." Once you have gotten through the company's phone tree and you are talking with a customer service representative, explain to them what you are looking to do. They will be able to tell you if you are eligible to have your cable box reactivated, and if you're not, what you will have to do to become eligible. If you are behind on payments, make sure you have either your credit card or checking account information available so you can pay your bill.
Confirm cable box reactivation. The easiest way to be sure your cable has been turned on is by turning on your TV to channels that only come in via your cable box. Stay on the line with the representative while you do this; you don't want to have to call back and go through the phone tree again if the reactivation doesn't work. If it doesn't work the first time, the representative may have to try something else to get the connection going again.