Windows – How to logon to a non-domain computer from one in a domain

The fact that you get an IP address and can ping the router, means your network is up. If you cannot get outside the network, then likely your LAN settings are configured to go through a proxy, probably a left-over configuration from when on the domain.

First make sure you are not on the domain anymore: Right Mouse Button My Computer, Properties, on the "Computer Name" tab click the "Change" button to 'rename this computer or join a domain', and check it is on a workgroup, and not on the old domain:

Then make sure you don't try connect via a proxy (some domains have this setup). From Control Panel access Internet Properties, on the Connections tab, in the LAN settings check you are not connecting via an old proxy (from the previous domain setup).'

Turns out the domain had a policy in place to only use NTLMv2 (as expected for stronger security), of which Windows XP will not use by default. I had to make the following registry change on the non-member computer to use NTLMv2. Local Security Policy is not available to make this change, as it's the home edition of Windows XP.

Registry path: HKLM\System\CurrentControlSet\Control\Lsa Setting name: LmCompatibilityLevel

Default value: 0 (Clients use LM and NTLM authentication, but they never use NTLMv2 session security. Domain controllers accept LM, NTLM, and NTLMv2 authentication.)

Required value: 5 (Clients use only NTLMv2 authentication, and they use NTLMv2 session security if the server supports it. Domain controller refuses LM and NTLM authentication responses, but it accepts NTLMv2.)

More information on this setting

The non-member computer now accesses SMB/CIFS shares on the domain instantly using the classic "create the same local user on the domain with the same password" trick.