new site install into subdirectory problem

I have a couple of existing sites and have recently registered a new domain which I would now like to add wordpress to.

A couple of months ago, I successfully installed wordpress onto this new site and it worked fine, but I have since forgotten all the login details. In a moment of madness, I got annoyed and so I deleted the files and thought I would run a fresh install instead, because I thought I knew best and that I didn’t need to ask for help to retrieve the information. How stupid of me, because here I am, after having spent much longer trying to fix whatever I’ve done.

So, in my fit of rage I deleted the database and user, deleted the correct subdirectory with the installation of wordpress, unassigned the domain from my master account and decided to try and start fresh, as if it was a brand new domain that I purchased today. So I created a new subdirectory, unzipped wordpress installation files, followed the usual manual installation instructions; created new database and user (with full privileges), changed the wp-config.php file to include the API key and the new database and user details, etc.

Once I finished the normal instructions, I added the domain back in as an addon domain and assigned it to the subdirectory I had just created, but I had to change the name of the subdomain, because apparently the original one is still there (I must not have deleted it) and is linked to a different sub directory.

At this stage I can normally access the wp-admin/install.php page and enter the details to get things up and running, but instead I am getting 403 permission denied. I have checked permissions on the files and made them all 775 temporarily, but no change.

I have clearly messed something up here, but I can not see what. I have experimented with creating new users and changing the API keys, but I am stuck.

Please please help