Unable to alter or remove password.

When I attempt to alter, remove or change my primary password under the users interface I receive an error that windows is unable to change the password. I can create a new user, create, alter and delete it's password. I have also noticed that I have a "switch user" button below my name when I start windows, or return when screen save is active and my user name is locked unless I use the "switch user" button. I have just also been locked out from logging on to the same computer as the only user visible was the primary user (mine) and that account was locked. The system finally let me on after I left the login screen for about 5 mins, it then accepted my password and let me log on.I have not altered any settings in passwords or administrative local security.Can someone suggest a solution?I have also discovered that I am unable to create a password disk as the password I have on my account is not recognized by windows.