wordpress does not install

I set up the wp-config.php files according to step 3 and then uploaded all the wordpress files to a subdirectory called blog on server. When I put the http://rachelhuggett.co.uk/blog/wp-admin/install.php I get the the following:
Warning: require_once(/home/www/rachelhu/blog/wp-admin/includes/upgrade.php) [function.require-once]: failed to open stream: No such file or directory in /home/www/rachelhu/blog/wp-admin/install.php on line 21
As I can see the files are on my server I do not understand what I can now do to make the install successful.
Any help much appreciated.