If everything else is as it should be under Sound and under Devices but you still have no sound through your USB devices and you have no reason to suspect the devices themselves, then completely power down your notebook for a few minutes. Then, with the device plugged into a USB port, restart your notebook. The USB device should get recognized on startup. Note: a mere "Restart" style reboot won't work to get your device recognized. You have to completely power down and stay down for a few minutes before powering back up for this to work. It works everytime for me.