password problem on my HP Pavillion tx 1000?

When turning on my HP Pavillion tx 1000 laptop, which uses Windows Vista. When I go to log onto my account,a Windows Security message comes up, prompting me "the user's password must be changed before logging on the first time. When I click the "OK" button, it kicks me out, never allowing me to change my password. I have had this laptop since bought new a couple years ago. never had any problems like this before. This also happens to be the adminstrator accoun, so I am pretty much shut down til I figure this out....any ideas?