you tube music

No, you can't use ALL music on YouTube. Particular artists like Metallica and even Gym Class Heroes specifically ask YouTube NOT to post their songs or have people be able to listen to them online, and YouTube legally HAS to honor their request.

The only way around it that I see is that you could try to find a live version of the song, or do a realistic-sounding COVER of the song and post it as the music. Live versions & covers are NOT usually copyrighted.

Yeah, they're doing that now, I made a video with pictures of my daughter and it had Alicia Keys song "if I ain't Got you" and it got muted because it's copyrighted, then they give you choices to pick another song to replace it, but the songs they have suck! I couldn't find any song that I like.

At all costs, avoid copyright material. If your advert is any good, surely it can stand on its own, without a soundtrack (though I agree that the right choice of music helps)!

I have come across advertising vids where the track they chose is just so off-putting that I put that company on my list of never-go-there-again-whatever after 15 seconds. It depends what you are advertising but (and you might try it as an exercise) a relatively soothing, slow and innocuous track will generally get more sales than an upbeat, lively (and, perhaps, controversial) one.