I'm assuming you re-booted your PC, right?
Do you have a graphics or sound card too? The sound output might have inadvertently switched to another source.
Right-click on the little sound icon on the bottom right and go into sound settings. Then make sure you have the proper sound output device selected.
If worse comes to worst, go to device manager and remove the sound driver. Google for the latest driver and install that instead.
Good luck...don't blame me if your PC blows up