For Windows only:
Go into user accounts (control panel --> user accounts) and then change your profile/user ID's password. Generally if you didn't enter one the first time you used Windows and the second boot up will ask you if it should stop asking, and most people click yes if they haven't entered a password. If you change the password to anything (because it is currently set at nothing at all), it should resume prompting you.
For Networking:
Go into your network properties (control panel --> network) and change the logon from 'Windows Logon' to something else.