I just fixed this problem on Lenovo laptop. My computer could see the USB sound card, I could never get sound from it. If this is your problem, go to Synaptic and down load pavucontrol. This is the control panel for pulse audio. After you download the program look in the Multimedia in the Applications menu and 0pen the program called Pulse Audio Volume Control. Open Output devices. Your USB sound card should be visible as well as the build in sound card. You turn a sound card on or off by clicking on the speaker symbol. Click the speaker symbol to shut off the built in sound card, and click the symbol to turn on the USB sound card. Do the same in Input devices. If you are trying to use the sound card for an application (like VLC), start VLC and look Playback. VLC should show there. A drop down menu should allow you to choose between sound cards.
If you already have pavucontrol installed and/or none of this works, I am out of answers. This is the best I could do after a couple of weeks of searching.