Can't install wordpress, other plugins.

I am using WordPress 3.3.1. I am unable to reinstall a clean version & get the following message:
Downloading update from http://wordpress.org/wordpress-3.3.1-no-content.zip…

Unpacking the update…

Warning: copy(/home/content/64/7647164/html/wp-admin/includes/update-core.php) [function.copy]: failed to open stream: Permission denied in /home/content/64/7647164/html/wp-admin/includes/class-wp-filesystem-direct.php on line 200

Could not copy files.

Installation Failed

The Plugins doesn’t list any Plugins at all.
The Editor says that there are no Plugins installed on this site
When I try to Add New & reinstall Aksimet, as an example, I get the following message:

Downloading install package from http://downloads.wordpress.org/plugin/akismet.2.5.5.zip…

Unpacking the package…

Installing the plugin…

Destination folder already exists. /home/content/64/7647164/html/wp-content/plugins/akismet/

Plugin install failed.

I have no idea what I may have done to cause this but it seems more likely that I have screwed up somehow. I’m not very experienced a building websites.