1. if you have installed a domain (adds) roll then the default setting is password expires after about 30 or 60 days... I always remove this setting on my server account.
p.s. if you have adds installed then you are logging in as an domain admin, not a local one... the account gets upgraded as part of the install process with the same settings as the local account had. This is an issue because once adds is installed on any Windows server you can no longer change local account settings... the only option is to un-install adds and then set your local account settings.
2. if your domain password has expired you will be promted to change it at the next logg-in... you type the old password and it asks you to enter a new one, that must be different. The default setting is 1 cap, 1 number and 1 symble so Pas$w0rd would work as would Pas$w0rd01 but again these settings can be adjusted before the adds roll is installed.