Buzzing when useing playback

Im, new to cubase and while trying to figure out the basics I have found my playback is buzzing.
I use a TV with a hdmi as my monitor and I use a set of speakers put into my computers line out. Sometimes when cubase says these speakers are connected and active no sound comes out.

But the bigger problem seems to be that if I have ANY audio output is in while recording my guitar, then use the play back I get a buzz that makes the recording useless.

But if I have no audio out put in when I recorded then connect it up after it plays fine.

Im sure its something to do with my acutally soeakers and not the recording. Any help would be appreciated, this is most likey me not haveing a clue so I apologize in advance if its my own stupidity.