I try to log into my dashboard, and I get looped back onto the wp-login.php page

Hello! Okay, so I’m at my wits’ end over here. So is the poor Support person from my webhost, I think. He pointed me over to the Login Troubles section on the Codex over here, and I did everything listed on there.

I still can’t log into the dashboard, even after doing a clean install of WordPress yesterday night (and killing all my posts in the process) and also repairing the MySQL database assigned to my site (even though there was actually nothing to repair). Hell. I even created a new database. It still doesn’t let me in. I’m absolutely stumped right now, and I’m hoping the community can help me out…

Oh for more reference to my problem, this was what I told the Support Dude from my webhost:

This is my problem: I can’t log in to my website (LeaniAuxilio.com). I mean I can access the wp-admin page, but when I try to input my username and password it redirects me to… my wp-admin login page, as if I didn’t ever put in my username and password.

My two other addon domains, NinotchkaRosca.com and JustCliqIt.com are just fine. I can log into them just fine. LA.com… I have no idea what’s wrong. I’ve tried:
-tweaking the wp-config file (obviously didn’t work)
-checking the .htaccess file (nothing looks amiss to me) and then looking my database tables through phpMyAdmin if there’s anything wrong (there was none)
-disabling my plugins and themes
-doing a fresh WordPress Install (just yesterday)
-and making a new MySQL database, and having LA.com point to it. It still didn’t work either.

Please help me out. I really can’t figure things out right now, considering I currently have to deal with Drupal migration issues at my workplace as well. Gah. x___x