I have Scarlett 2i2 by Focusrite, which is a simple instrument/microphone interface and I'm trying to get it working on a Gateway NV53A laptop. 

The interface driver is installed and under Control Panel > Sound the LINE IN and LINE OUT are set as the defaults and the built in is set to Disabled.

But the laptop's built in microphone is the one that's working and a microphone plugged into the interface isn't working. How do I make the interface mic the default if not as above? 

Same is true of playback, instead of going out through the interface, the built in speakers are playing the sound.

Thanks - rev

(I'm assuming the USB cable is carrying the sound and not just being used to power the interface? - I've been reading the manual but I have come across confirmation of that).

You must have the Scarlett selected as the Recording and Playback timing master in Sonars Options-dialogue, and also in the in/out drivers window. Do you have ASIO-drivers for the Scarlett? I assume they should be available. You can't control Sonars inputs and outputs in the Control panel.

Kalle:

Thanks but Sonar was not involved. The person using the laptop drags an mp3 backing track into Guitar Rig's Tape Deck and then sings to that track live in restaurants. 

I haven't read anywhere that the Scarlett has to have a specific application, do you know for sure that it does?

Clear enough. None of that was explained in your original post, so I assumed you're trying to use Scarlett with SONAR, as this is a SONAR forum. The soundcard specific ASIO drivers are the most essential and important part in making a soundcard work fluently in DAW work.

Someone else surely has solution ideas for you.