wp-admin folder not reachable after new installation

I have just done a completely clean installation to a new folder on my site. I could only get it to work at all by copying a .htaccess file from another installation in another folder but now I can’t reach the wp-admin folder at all.

You can see what I mean here:

https://9012live.com/ works just fine – all posts, comments etc. etc. but try and click on the admin link – https://9012live.com/wp-login.php and the address bar displays – https://9012live.com/not_found/ and the page doesn’t change.

My host is 1and1 and specifically state that they don’t support DIY installations of WP at all.

Please help!

Incidentally, I have done this process 3 times previously in different folders on my site and it worked fine each time – that was with older copies of WP, however.

Thanks!