go into network properties and see if it's set to load with 'client for microsoft networks' or if it's set to 'windows logon'
if it's set to 'client' then you should change it to 'windows logon' and reboot. when it prompts you for user name and password, just put in a user name but NO password...then next time it won't ask you
if it's already set to 'windows logon' , then you should go into control panel..passwords. and (assuming you know the password) change the password to nothing. then, after a reboot, it will prompt you and when you just hit enter (for no password) it will not ask you again
last but not least, if it says 'windows logon' but you do NOT know the password, there are ways of resetting it. let me know and i can tell you how
hopefully this will help