Tearing hair out!

I've downloaded punbb.

Created a mysql database with a password and login through my hosting control panel.

I've uploaded the contents of the punbb 'upload' folder to the folder on my webspace i will be hosting the forum in.

So far so good.

I then went to the install.php phase, inserted the necessary details, received the generated php script ok.

Used Dreamweaver to create a blank php file and pasted the generated info into it, saved it as config.php.

I then uploaded the config.php file to the forum root directory and proceeded.

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<?php

$db_type = 'mysql';
$db_host = 'localhost';
$db_name = 'myforum';
$db_username = 'admin';
$db_password = 'password';
$db_prefix = '';
$p_connect = false;

$cookie_name = 'punbb_cookie';
$cookie_domain = '';
$cookie_path = '/';
$cookie_secure = 0;
$cookie_seed = '20328a26';

define('PUN', 1);

The file 'config.php' doesn't exist or is corrupt. Please run install.php to install PunBB first.

------------------

I've checked my forum folder (via ftp) and the config.php file IS there. When I click the link to re-run install.php I get this message

The file 'config.php' already exists which would mean that PunBB is already installed. You should go here instead.

When I click 'here' I then get punted back to the first message.

I've been trying to sort this for 2hrs and tearing my hair out.

Any advice would be greatly received.

Lesley.