Hi,I think the usb phono preamp also uses your soundcard as well, so try checking their settings to make sure nothing is muted etc,and set all sliders to about 65%.
Also try Volume Contol / Options from Start menu / Progs /Accessories / Entertainment.
Its also worth setting your display settings to 24bit or higher, as this makes various other features accessable. Hope this helps ,(Im using Win Me by the way). cheers.