As an uneducated singer that is a problem I have run into time and time again. Musicians who know waht they are doing tend to ask what key I use for a song. But I don't know! My music comes from the heart and comes out of me at a key that sounds good in my head and fits into my vocal range.

Which brings up another point. Music must be one of those areas where the practitioner doesn't need to know what he's doing to succeed. There are plenty of successful (i.e., making a living on music) singers out there who don't know one key from another. They depend on their co-musicians to tell them. I can't point fingers because I am one of those people but then, I've never tried to make a living with music.