"Getting Sound from the Computer, But No Sound from the Turntable
Go into the Ion's Audacity software and select "Monitor Input." It's tricky to find but if you take a good, hard look under the level meters you will see a microphone icon; next to that there is a downward pointing arrow icon. Click on it and select "Monitor Input." and you should now hear sound."
which rings a bell from when I was using the Ion USB turntable to convert a load of vinyl.
Read more: Best Way - Ion USB Turntable Troubleshooting | eHow.com click here