This is an area that a lot of people have problems with. If you are not able to log on, check the old Caps Lock key. Turn it off, if it's on, and try again.
Some systems require that passwords change at regular intervals.
Make sure you are using the newest password if it changed recently. Most networks will temporarily disable a users account if it encounters several unsuccessful logon attempts. This is to foil would be hackers. If you are unable to successfully logon after five tries, check with your network administrator to see if your account is locked. A quirk with Windows 95 and 98 is that users logging on to a system for the first time are required to give their password twice.