Have you tested other webroot than
$CFG->wwwroot = 'http://moodle/moodle';
(try to use http://localhost/moodle or http://ip-address/moodle )
The only other idea that I have is that you could download the package once more (delete the old files and drop database/tables) and install it again. Sometimes files are just corrupt or some files are missing (for example after ftp transfer).