Even I accept answer the accept rate is displayed as zero.I dont know why?
The accept rate is only updated periodically, I believe - if you've accepted an answer just now then wait a while and it should update.
Also if you accept a CW answer, I don't believe that affects anything.
If you could let us now which account you're talking about, that would help :)
EDIT: Okay, having looked into it a bit more, and found the original blog post I think the problem is that the questions are too new.
You've only accepted answers to the new questions - whereas only questions 3 days old (or older) count for either acceptance or non-acceptance.