When you add an interface to your system, the interface replaces the on-board sound of your computer.
Generally, though, you have to tell your computer to go to it rather than its own.
Do you get sound coming through the RT2? Can you record ok through the RT2? When you play media (e.g. youtube videos), doesw it play through the RT2? If answers are all 'yes', then you are fine. If answers are 'no', you may have to investigate changing some settings.