Welcome to Android Central! Are you saying you're unable to get Hangouts to give you notifications for messages? Open Hangouts, tap Menu then Settings, and select your Google account. You can adjust notifications for any Hangout messages here. If you tap Menu/Settings, and then tap SMS, you can adjust notifications for SMS messages.
For particular Hangouts or SMS conversations that are ongoing, you can select whether or not to be notified of new messages by selecting that thread, tapping Menu, then People & Options, and checking or unchecking Notifications.