The issue you are seeing with Nero Burning ROM not working has been resolved in the current version of Nero 18.104.22.168 posted on our website. You can use the below link to update to this version.
As for your audio files not playing, are they files you purchased from off the website using services such as Napster, iTunes, MusicNow, etc?
If they are, then the problem is that Nero Home and Nero ShowTime do not yet support checking license for DRM protected audio content. We will soon be implementing this feature in Nero Home and Nero ShowTime.
You can confirm if this is the case, if you launch Nero Express or Burning ROM, select Audio format, add one of these audio files and play from within Nero Express or Nero Burning ROM. These programs should work as they do support DRM content already.
NeroMix has been discontinued, as we do plan on rolling many of it's capabilities into Nero ShowTime in the near future.
The idea is that you would use Nero Home or Nero ShowTime to play content.