Wave Slider - Volume Control

Hi

I have just installed a new sound "interface": a Presonus Inspire. Everything is working fine apart from the following:

Every time I attempt to establish a voice chat in MSN messenger, the wav slider in volume controls will automatically slide to the bottom leaving me with no sound. As a result I have to access the volume control to move the wav slider up. Also whenever I adjust the volume of my mic in MSN messenger chat, it knocks the wave volume down again.

In Audio and Video setup in MSN messenger, I test the sound on the sound test page and I can see the volume slider being knocked down to zero. Everytime I attempt to move it up (to hear the test sound) it automatically moves back down to zero.

This is literally doing my head in. Can anyone help? I'm guessing this problem will crop up with other things besides MSN too.