PC speakers dont work after using usb headset

My speakers used to work on my HP desktop. After using a USB headset wwhich still works on the PC, the speakers no longer work. The speakers do work on another computer. The HP Windows 7 computer says no audio detected and the speakers are not found under Manage Audio Devices and the Sound Video and Game Controllers is nowhere to be found under Device Manager. Speakers and volume are on and pugged in correctly. Any ideas?