Hi,
have you installed the driver? If not, you download a copy here: Link Removed
Try installing the driver for win 8, if no win 8 driver then try the win 7 driver. If it still doesn't work then right click the win 7 driver, click properties and then choose compatibility mode for windows 7.
Have you tried setting your default sound device using the way outlined in the screenshot below?
there is no official win 8 driver for dany u-2000. but win 8 automatically update itself latest driver. and realteck is already my default playback device
Try un-installing the driver win 8 installed but before doing so make sure you change your windows update settings to 'check for new updates but ask me whether to download and install them'. Then, download the Windows 7 driver and try the compatibility mode mentioned above.