If you are being prompted to enter your serial number when opening your actively subscribed Creative Cloud application then there maybe missing account information. Please see Creative Cloud products prompt for serial number on launch | CCM - http://helpx.adobe.com/creative-cloud/kb/ccm-prompt-serial-number.html for additional information.
In addition if you are facing difficulties reaching the activation server please see Sign in or activation errors | CS6, CS5.5 Subscriptions, CS6 Perpetual - http://helpx.adobe.com/x-productkb/policy-pricing/activation-network-issues.html. Also if you are managing a network please see the Adobe Creative Cloud Service Access Documentation for IT section of http://www.adobe.com/devnet/creativesuite/enterprisedeployment.html.
Finally for additional information on managing your Creative Cloud account please see Manage your membership | Creative Cloud - http://helpx.adobe.com/x-productkb/policy-pricing/membership-subscription-troubleshooting- creative-cloud.html.