One’s ability to sing depends on many factors working together (that is, your body is working in harmony). Probably the biggest cause of not being able to sing is a malfunction of one of these factors (thereby causing non-harmonious sounds).
To name a few:
- The connection between your hearing and your vocalizing.
- Your mind’s perception of your singing.
- The control of your vocal tract.
- The understanding of your vocal tract.
- The audience’s hearing.
- The type of music.
- Body tensions.
- Understanding of harmony.
- Singing emotional interpretation.
- All the other things mentioned in the above postings.
- The voice itself—this may be worth only 40%, in light of the above. (So, yes, if one is genetically gifted, he is 40% ahead.)
Rod Stewart, Bob Dylan, and Louis Armstrong both have awful voice, as well as Nancy Sinatra—they did well though.
If you’ve tried all the other things mentioned in above postings, then this says you haven’t found the malfunctioning piece. My guess is that what’s missing is somethings that is not well taught in standard singing methods.