How do I fix the "Internal Server Error"

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Javascript

PHP

Ajax

MySQL

jQuery

I have a feedback form in my webpage, All I need is to make the user fill those fields(Name, Email, Contact No, and Feedback) and to click submit button. When he clicks the submit button after filling all these fields the data should be mailed to an email address (I have defined it in the code).
I have done everything and its all working, but when I host my site and submit a feedback it shows "Internal Server Error".
Plz help me in this scenario..
Thanks in Advance