I am running php 5.2.9-2 and mysql 5.1.58 on a windows 2000 server box and wp 2.9 and 3.0 both work fine. When I upgrade to 3.1 or above, I get a login loop where after I enter the correct user and password, I get redirected to the login page again. This happens if I do a fresh install of wp 3.1 and above as well. I've tried many of the solutions I found through google including using a new database, clearing cookies and cache, renaming the plugins folder, adding @define(‘ADMIN_COOKIE_PATH’, ‘/’); to wp-config.php, I'm not using htaccess as far as I know, I am not defining siteurl or home in wp-config, and am not running multisite. I've tried just about everything. Any suggestions?