It's easy to take your question with two different approachs - verifying the hardware is connected correctly and then making sure the audio driver is selected in the software.
With Firewire interfaces, the best way to verify that your device is connected (PC and Mac) would be to use this article below. It helps you recognize if the device is connected and functioning (i.e. firewire card/cable/mixer is communicating) and also helps you recognize when the driver is mounted and seen by your computer.
How Do I know my StudioLive (Ai) is connected to my computer and functioning over firewire?
The second half would be making sure that your driver is selected on the interface. A common message seen on Capture 2 software would be "Cannot create new sessions if the audio device is Stereo." This means that the device driver is not working correctly. Mentions of this are found on be below article, including how to select the driver for recording on Capture 2.
What does "Cannot create new sessions if the audio device is Stereo," mean?
If you are still having issues after doing the above, please Contact Technical Support for further assistance.