Can't Log In

Gallery version (not just "2"): I can't log in so how can I find this out?
Gallery URL: http://www.falmouthmass.us/gallery2/main.php
PHP version (e.g. 5.1.6): 5.2.2
PHPInfo Link (see FAQ): http://www.falmouthmass.us/info.php
Webserver (e.g. Apache 1.3.33): IIS 6.0
Database (e.g. MySql 5.0.32): MySQL 4.1.12
Activated toolkits (e.g. NetPbm, GD): ?
Operating system (e.g. Linux): Windows server 2003
Browser (e.g. Firefox 2.0): Firefox 3.6.12, IE 8

Our installation of Gallery 2 has been running unchanged for a few years. I think the last time anyone logged in to it was a year ago. I don't think there have been any changes to the system since, but...

I can't log in to any Gallery account: user, administrator, newly created.

Where do I start?