plugin.php error

hell sirr…
i m using WP ver. 3.3
with CPANEL

i have some problem with my website… my homepage shows following lines..

Warning: require_once() [function.require-once]: Unable to access ./admin.php in /home/heavenof/public_html/wp-includes/plugin.php on line 11

Warning: require_once(./admin.php) [function.require-once]: failed to open stream: No such file or directory in /home/heavenof/public_html/wp-includes/plugin.php on line 11

Fatal error: require_once() [function.require]: Failed opening required ‘./admin.php’ (include_path=’.:/usr/lib/php:/usr/local/lib/php’) in /home/heavenof/public_html/wp-includes/plugin.php on line 11

and my WP-ADMIN page shows …..

Fatal error: Call to undefined function current_user_can() in /home/heavenof/public_html/wp-includes/plugin.php on line 20

plz give me some suggestion for resolve this problem.!!!

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