This could be due to a couple of reasons:
Your subscription may no longer be active. Log in to the Online Account Center to check the status of your account, view and pay your bill, and manage or reactivate your subscription. You can also compare different plans at www.siriusxm.com/plans.
If you are missing channels or have recently subscribed, you may need to request a refresh signal. Be sure to have your Radio ID handy.