I have had problems similar to this.
Two suggestions:Suggestion 1 - Check whether part of Windows Networking is Not Installed or Turned Off
I had a similar problem a few years back.
It turned out part of Windows Networking had not been installed by my laptop vendor - somehow!
All the network protocol stacks (IP, Client for Microsoft Networks) were there, but something more obscure like the Workstation service was missing.
The fix was something like inserting the XP CD and installing networking again.
Perhaps check the Workstation service is present and running on all computers, or further investigate this line with a few Google searches.
Sorry to be so vague! Suggestion 2 - Check the Sharing and Security Model
1. Log in as 'administrator' (or some other user with administrative privileges) on your laptop.
2. Go to "Start" > "Control Panel".
3. Open "Administrative Tools".
4. Open "Local Security Policy".
5. Open the "Local Policies" folder.
6. Open the "Security Options" folder.
7. Scroll down and double-click "Network access: Sharing and security model for local accounts".
8. If this says "Guest only - local users authenticate as guest", change it to "Classic - local users authenticate as themselves" and press "Ok".
Why this may work: If your computer is using the "Guest only" model, all incoming share connections will use the privileges of the Guest user. The Guest user may not have any privileges to access shares on your computer. By changing to the "Classic" model, all incoming share connections authenticate as the user making the request (or another supplied username), and this non-guest user can be granted privileges to access your shares.
Let me know if this helps,