After 3.0 upgrade can't login

Hi, after upgrading to version 3.0 I can’t log in to the admin panel. I use the same template for all of my blogs this issue happened to three of them. After upgrading to version 3.0 I logged out and went back to the log in page and attempted to log in and access was denied. Not recognizing any info that was originally set up.

I have been a WP user for many years but I am not a skilled coder by any means.

Would appreciate any help.

Thanks