Check your power. If you're running too many things off the pi, it may be drawing too much power to supply everything. Mine all runs off a 5v power supply, but I did try to run everything through a USB hub that wasn't powered, and I was having similar issues. A powered USB hub should be the way to go, that way your screen and your pi can be powered independently. If it's actually USB sound card then it still needs to be connected to the pi, however if it's just USB powered then that can be supplied on it's own. Mine has a USB cable, but it also has a standard 2.5mm jack to supply the audio, the USB cable is just to power the speakers.