Warning: array_keys() [function.array-keys]: The first argument should be an array in /wp-includes/theme.php on line 521

Warning: uksort() [function.uksort]: The argument should be an array in /wp-admin/includes/class-wp-themes-list-table.php on line 48

Warning: array_slice() expects parameter 1 to be array, boolean given in /wp-admin/includes/class-wp-themes-list-table.php on line 55

Cause : You would have messed up with folder name themes and its permission.
Fix: Get the permission and folder name corrected if you have renamed it with some other name by mistake. If its already fine then get the same wordpress version and replace wp-content folder unless you have customize plugins and themes. If you have customize then you need to redevelop it.