Still having problems logging in – gettin 404 Http error page

I still can’t access my wordpress blog administration panel, plus all links on my website to the main index page of the blog are giving the 404 Http error page as well.The link I normally have to the blog is:
https://www.gowerphotography.co.uk/Blog/index.php
This link produces the 404 error page. If I type in:
https://www.gowerphotography.co.uk/Blog
the blog appears. Any ideas?
When I try to login using the following address:
https://www.gowerphotography.co.uk/Blog/wp-login.php
I get the 404 error message as well.
My server is running PHP4.41 so I can’t update WordPress to 3.03. I did download it and used the index.php, wp-login.php and wp-admin folder to replace the original files on my server in case they were corrupted. I haven’t added or updated any plugins for a month and access to the site was fine 7 days ago. I have removed all the plugins and attempted to access the site, with no change to the problem. The website directory hasn’t been changed or moved.
Any ideas would be appreciated, thanks in advance.
p.s I’m not a techie, so simple explanations required!