LCD TV has picture but sound issues?

I have a Samsung LN46A540 LCDTV. The picture works but the sound doesn't work from the tv speakers. However I plugged a pair of speakers to the headphone jack and it works from there. Where do you think is the problem? Is it a cheap fix I can do myself? Thanks

Oh .. This might be a separate unrelated issue but there are times when I get vertical rainbow streaks on the screen. It goes away after I leave the tv off for a while. Any help with this is appreciated. Thanks!