Once you update to Windows 8.1, the Messaging app will be gone all together. Windows Live Messenger has been shutdown for months now, so to talk with those contacts you will need Skype as bassfisher mentioned. If you mean to start an email conversation, you can use the Mail app. To chat with Facebook contacts in Windows 8.1, you'll need the Facebook app. To get Windows 8.1, ensure all the latest Windows Updates have been installed, and then open the store app where it should be the first option presented to you for download.