another thing that beginning guitarists should consider when using the metronome...when a song is at say 120BPM (beats per minute) you most likely wouldnt be playing that song that fast, especially if your a beginner.
Its always best to slow it way down to say 60-70bpm and once you can play it comfortably at that speed, you can then work your way up to the actual song speed. It's a pain in the butt to do but it works.