I see from your previous post that unplugging and re plugging did not work.
Are you connected directly to the computer or using a USB hub?
Have you tried different USB cables?
Also, have you tried uninstalling/reinstalling POD Farm 2.5?
Line 6 Customer Support
If you are getting levels on the meters within POD Farm then your POD Studio GX is working just fine. What you need to do next is make sure that you are connecting headphones or speakers to the headphone/line out on the back of your POD Studio GX.