Not sure. Could be a number of things.
What error message are you getting? Does it say the email is sent, but the email never gets there? Does it not even send the email? Does it even TRY to email it? Do you have a mail server set up? Are the parameters correct?
Your question is too vague... please try to narrow down what the results are, and let us know what you have done so far to try to fix the problem.
And don't use
to show us your code. Use
instead.