Server Error

[REBEL21]

Every time i try to post on my website i get this error why? and how can i fix it?

Internal Server Error

The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator, webmaster@jamiesrebellion.co.cc and inform them of the time the error occurred, and anything you might have done that may have caused the error.
More information about this error may be available in the server error log.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

Please help fast!!

Regards,
Jamie
----------------------------------------------------------------------------------------------------------------
Edit:
please will somebody help me as i need this fixed ASAP!!!
Edit:
Just read that it might be the .htaccess file will somebody fix it QUICK!!!!
Edit:
Will somebody help me please, need this fixed!! how long does it take??
Edit:
Hello will any one help i posted this yesterday and have still got no reply!!
Edit:
Ive been waiting for hours and still waiting for help so please HHHHHEEEEEEEEEEELLLLLLLLLLPPPPPPPPPPPP!!!!!!!!!!!!!!!!!!!!!!!!!!!