IS this machine a dc? Is it a small business server? Have you “hardened” the server?
logged into the server locally as a local admin can you see the shares via \\127.0.0.1 ?
Can you access them? Can you access \\127.0.0.1\c$ from the local machine logged in as a local administrator?
Are the non domain users on another domain? Have you configured security between the two domains?
If you create your own shares can you delegate security to non domain users and access it or not?
Come back and update this and I will do my best to help you out!