
turn off "simple file-sharing". creates more trouble than it's worth. just seems to break the standard file sharing - including using the default share along with being able to specify a user account logins while networking to other machines.
Open Explorer, click Tools, Folder Options. Click View. Scroll to the bottom. Uncheck "Use Simple File Sharing (Recommended)".
i say, not recommended.
not using a domain? you can also set up network user credentials ahead of time...
control panel | user accounts | pick account... | manage my network passwords
just add the machine name, machine\user, and password. will speed things along if you always use the same accounts to network between machines.