Can't get past login, tried all the stuff WP suggests

I installed WP on my main domain and played about with it. All working fine, but I decided I wanted my blog on a different domain name so set this up with the same host as my main website. I downloaded WP (via Fantastico) onto this 2nd domain, all was working fine and so I designed my theme, and posted a couple of things. Came back to it after a couple of weeks to add but can’t log in (I know login details are correct as I received an email from them). Also, all the design work and posting I did has disappeared.

We’ve tried doing the cookie and plug in stuff. We’ve reinstalled the wp-login.php file on the cpanel file manager but nothing is working. Tried getting a new password but the link they sent doesn’t work!

I’m wondering if this is getting mixed up somehow with my primary domain, as if I simply go to http://www.mentor-coach.co.uk (2nd site)it has the default WP design and also my primary domain (throughtheforest.co.uk).

Help!! I’m not v technical so hope my explanation makes sense. Thank you!