Can't log in to webpage.

[Doulos]

I am running php-nuke 7.6 patched to 3.1. Everything was fine until today when I tried to log on and I just get returned to the home page. No matter what link (within php-nuke) I click, it just returns me to the homepage. If I click on a link that takes me out of php-nuke it works fine. If I try to go to the admin page, NukeSentinal asks for and accepts my username and password, but when I then try to enter my username and password into the admin page it returns me to the admin login page with no error message saying 'username and/or password' is incorrect.

Is this a php problem or php-nuke problem? or what?

Any ideas would be appreciated.

Thanks http://www.doulos-usa.com