500 internal server error message and problem

`Hi there, my site http://www.annanuttall.com and I just went to look at it and I got this:
<blockquote>Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator, webmaster@annanuttall.com 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 500 Internal Server Error error was encountered while trying to use an ErrorDocument to handle the request.</blockquote>
Any idea on how to fix this? I can’t log into my wp-admin area and I can’t even get into my website cpanel.
I heard this might have been cause by a plugin that allowed hacker to get in – how do i fix this?
I don’t want my site to be hack and for me to loose everything.
Thank you.

Please help me I’m tearing my hair out right now.