Samba share not visible from Windows 7 PC, even though UNC authentication works

I'm running XBMCBuntu 12.10 on an HTPC with the server hostname 'SCREEN', and trying to setup Samba to allow access to a share called 'Movies' by mapping username/password credentials to a unix user account (I don't want to allow guest access.) The name of the user is 'user'. I am able to log into the samba server from my Windows 7 PC's via the UNC path \\192.168.1.103 or via \\SCREEN. I am prompted for the the username and password, and when I enter them, it accepts them. (I set this up via smbusers, mapping the password via passwd.) I know the security settings are correct because if I use incorrect credentials at the prompt, it gives me an error.

The problem is that I can't see the shared folder that I have defined in smb.conf. I.e. I just get a blank window in Explorer with no error. And if I try browsing directly to the share via \\192.168.1.103\Movies, it just says "Windows cannot access \192.168.1.103\Movies - Error code: 0x80070035 The network path was not found.". I have a few other observations that might be relevant:

• The config file in /etc/samba/smb.conf is blank. The one that seems to be applicable is in /usr/share/samba/smb.conf.
• sudo testparm -s smb.conf > smb.conf.good fails with -bash: smb.conf.good: Permission denied
• The /var/log/samba/log.smbd doesn't seem to contain any errors:

[2013/12/20 21:35:28,  0] smbd/server.c:1053(main)
  smbd version 3.6.6 started.
  Copyright Andrew Tridgell and the Samba Team 1992-2011
[2013/12/20 21:35:28.852983,  0] smbd/server.c:1109(main)
  standard input is not a socket, assuming -D option

My smb.conf:

[global]
   workgroup = WORKGROUP
   server string = %h server (Samba, Ubuntu)
   dns proxy = no
   log file = /var/log/samba/log.%m
   max log size = 1000
   syslog = 0
   panic action = /usr/share/samba/panic-action %d
   security = user
   username map = /usr/share/samba/smbusers
   usershare prefix deny list = /
   encrypt passwords = no
   passdb backend = tdbsam
   obey pam restrictions = yes
   unix password sync = yes
   passwd program = /usr/bin/passwd %u
   passwd chat = *Enter\snew\s*\spassword:* %n\n *Retype\snew\s*\spassword:* %n\n *password\supdated\ssuccessfully* .
   pam password change = yes
   map to guest = bad user
[Movies]
   path=/home/user/Movies
   browseable = yes
   guest ok = no
   read only = no
   create mask = 0777
   directory mask = 0777
   writeable = yes
   valid users = user