I can't acces my post page in the admin area, its showing 500 Internal Server Error!!!

I can't access my WP post and static pages, its showing 500 internal server error once I try to access it. How can I solve this? Site still under construstion but here is the statement:

The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator, 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.

Note please: The problem was showing from http://www.sisimiblog.com/wp-admin/edit.php i.e any admin menu that links to the edit.php gives the link.
url: http://sisimiblog.com