Cannot login to admin panel

I have had some serious problems with logging in to the admin panel.

I am running wordpress 2.7
php5
mysql 5
unix

logging in, the page refreshes and removes the credentials, but does not redirect to http://blogname.com/wp-admin/

This blog has NO plugins. I repeat NO PLUGINS, the directory is completely empty.

I have 3 other wordpress sites on this host with the same setup with no problems.

I have tried deleting cookies, disabling my cache, all to no avail whatsoever.

I have tried commenting out the define path info in the login file. No joy there also.

I am probably going to move this particular user and blog to tumblr unless I find some help here soon.

thanks.