Vestax VCI-300 Issues

Hi all, I am having a wierd issue with my set up.

Firstly let me just say that I absolutely LOVE this beautiful unit and the Mixes I am able to produce using it...However here goes:

In the Past..
I was using this unit with my old Dell Dimension PC, through my 5.1 Altec Lansing ADA995's..when connected via USB, the unit functioned well when running Serato ITCH, (however due to the processor being slow and various other reasons I purchased a new PC)..when ITCH was not running but the power on the unit itself was left on the unit would continue to 'act' as the PC's Sound Card...hence I would successfully be able to play Music through Windows Media Player, Youtube and hear all PC sounds etc etc through the speakers (as it was recognising it as a Sound Card - i THINK, correct me if I am wrong!) All this was possible without having to remove the 3x 3.5mm pins (which the 5.1 Speakers have) and connecting them to the PC Sound Card on the rear...

Now..
With my new PC set up, When I run Serato ITCH the unit runs perfectly, even better and faster than ever before on the Dell Dimension! :-)

...However all good things soon come to an end..and this is my predicament..when Serato ITCH is not running but the unit is left on as before and I try to play any music through Windows Media Player, Youtube etc etc I hear nothing! The only way for me to use the PC speakers as well just that, PC speakers I have to resort to climbing through the table and remove the 3x 3.5mm pins (which the 5.1 Speakers have) and connecting them to the New PC Sound Card on the rear!

When I go to the Control Panel and go to the 'Sounds and Audio Devices' option, go to the 'Audio' tab, under 'Sound Playback' the sub menu does recognise the 'VCI 300' but however will not give me any output as I used to get with the Dell.

Am I missing an obvious thing hear such as a check box needing 'checking' or 'unchecking' ?

- the master level on the unit is set to 'up',
- both faders on the unit are set to 'up', (however with the Dell set up this was not even needed as only the master level controlled all the volume)
- the crossfader is set to the middle position

I am totally baffled! Please help if anyone can as this is such a brilliant unit as I am mainly a bedroom dj, I would really love to have this function working again as it was so brilliant when I had my old PC..if only it wasn't so slow and had a much better processor and ram!